# Posts by MathMate

Total # Posts: 12,086

**math! again**

3)The factors of 4 are: 1, 2, 4 The factors of 5 are: 1, 5 The factors of 6 are: 1, 2, 3, 6 Then the greatest common factor is ?.

**Chemistry (Dr. Bob)**

Quite right Dr.Bob. Thank you for the note. It just doesn't decompose like that. Carbon is required to reduce the oxide. Namely 2Al2O3+3C -> 4Al + 3CO2 The electrolysis part is more to help prevent the formation of CO. However, as you said, the ratio of Al and Al2O3 ...

**Chemistry (PLZ HELP)**

Aluminium oxide: Al2O3. Molecular mass (approx.)=27*2+3*16=102 Aluminium: Al Molecular mass=27. Write down the equation: 2Al2O3 -> 4Al + 3O2 (electrolysis) So 2 Al2O3 molecules -> 4 Al molecules. 2*102 Al2O3-> 4*27 Al 204 : 108 Use proportion to solve for the final ...

**Maths**

You will need to describe how the two pulleys are arranged, as well as the two blocks. Without that, it is not clear how the system is set up. You can also opt to post an image of the diagram/figure.

**g.p.**

This might help you to learn about a.p. and g.p.: http://www.mathcentre.ac.uk/resources/uploaded/mc-ty-apgp-2009-1.pdf

**math**

Y-intercept is the point where x=0. From the given function, P=(6000-400x)*(x-2) we substitute x=0 to get P=(6000-400(0))*(0-2) =6000*(-2) =-12000 It also means the loss incurred when the manufacturer gives the paper away ("selling" at a price of x=$0 per ream).

**math**

Use Perimeter = 2(L+W) = 20 Substitute L (that you calculated) into the equation, and solve for W, hence L.

**Math**

If you buy 10 apples with $2. How many apples would you get for $1?

**Matrix application**

"Substitute each pair of x,y values to produce 3 simultaneous equations with unknowns a, b and c" As instructed, x = 150m y = 190.650m a(150)^2+b(150)+c = 190.65 a(300)^2+b(300)+c = 611.450 a(450)^2+b(450)+c = 831.141 Form matrix, A= |150^2 150 1| |300^2 300 1| |450^...

**Math**

Set up equations to solve for X=number of goats in farm x, Y=number of goats in farm y. "The ratio of the number of goats in farm x to the number of goats in farm y was 9:4." => X/Y=9/4 multiply by Y to get: X=9Y/4.....................(1) "After 35 goats were...

**math**

Fermat's little theorem says if p is prime, and p does not divide a, then a^(p-1)≡1 mod p. Here we put p=61, therefore 61 does not divide a=8. Hence 8^(61-1)≡1 (mod 61), or 8^(60)≡1 (mod 61). Recall the multiplication rule of modulus arithmetic, 8^120&...

**Math**

Assuming ACD is a line segment, then by the rule of line segments, AD=AC+CD => CD=AD-AC=20-15=5 If ACD is not a line segment, then please supply additional information/description.

**Algebra**

R=age of Rosa A=age of Amy then form two equations using information given: "Rosa is 14 years older than her sister Amy." => R-A=14 => R=A+14.................(1) "3 years ago, she was 3 times as old as Amy." Three years ago, both were 3 years younger...

**math**

Let long side = S (cm) then short side = S-10 (cm) A parallelogram has opposite sides of equal length, therefore the perimeter equals 2(S + (S-10))=4S-20 We were given the perimeter is 88 cm, therefore 4S-20=88 Solve for S (the long side) and S-10 (the short side).

**probability**

First find out how many distinct letters are there in the word MATHEMATICS, call this number "n". For example, the word SAILING has the letters S,A,I,L,N,G, 6 out of 7 letters are distinct, while the letter I is repeated but not counted more than once. In the English...

**Math**

Assuming the favourite and second favourite bands are distinct (different), then there are four choices for the favourite band, and (4-1)=3 choices for the second favourite band. Use the multiplication rule to find the number of possible votes.

**Math**

1826.11 (1826.11019) is the correct monthly payment to obtain 100,000 at the end of four years. Note that your formula assumes that payments are made at the end of each month. The interest is the cumulative amount at the end of four years less the total amount paid, namely 4*...

**Probability**

Sue, You don't have to change the screen name. It will be easier for teachers to work with the same person. It would be similar to your previous question (in the name of Paige), except that to get every answer wrong, you only have three choices (and the student must know ...

**Math-Probability**

We will assume that all the questions are independent of each other, and that each question requires exactly one choice. That is the instruction "indicate all that apply" will not be applicable. There are four ways to arrange the answers to the first question. There ...

**Stoichiometry**

Yes, the limiting reactant is CaCl2. Since it is a reactant, there is no new CaCl2 formed... unless you meant something else. The same idea extends to products. The overall molecular ratios are 1:1:1:2. So you can calculate amounts of products formed using the ratio.

**Stoichiometry**

Na2CO3 + CaCl2 = CaCO3 + 2NaCl Yes, the first step is to write a balanced equation of the reaction. The coefficients of the balanced equation tells us the relative number of moles of each reactants is required, as well as the relative number of moles of the products. In this ...

**Physics**

On an inclined plane, the forces acting on an object of mass can be resolved along the incline (+ up) as follows: Gravity force+Friction force =-mgsin(θ)+Ff The above sum equals zero if the object stays in equilibrium. Therefore Ff=mg sin(&theta) The above can be derived...

**Physics**

Since all numbers are known for m1,m2,g and θ, we can calculate that force pulling block up-plane = T = m2g=98.1 N Force pulling block down-plane = mg sin(&theta) =58.90 N The difference is due to friction, of the amount = 39.20 N I believe you answer is correct. Book ...

**Math (calculus) (mean values)**

Part (a) average rate of change is the difference between the end of last month to the beginning of the first month, divided by the number of months, so Average=(s(12)-s(0))/12 Part (b) Calculate the derivative of the function s(t), with respect to t: d s(t) / dt =d(1085-1395...

**Civil engineering**

Hint: https://en.wikipedia.org/wiki/Varignon's_theorem_(mechanics)

**Calculus**

Have you read the reply: http://www.jiskha.com/display.cgi?id=1480206573 ? If you have and it was not clear to you, would you consider posting a follow-up question instead of a new post?

**probability**

How many of the dvrs are NOT defective? If selecting any item from the inventory has equal probability, what is the probability of selecting any NON-defective item from the 50 dvrs?

**Calculus**

It all depends on the size of the units. If the mean of the y-values is, say, 100, then residuals not exceeding 0.6 is ok. If the mean of the y-values is 1, then it's not acceptable. Also, it is related to the number of data, and the sign of the residuals as well. For ...

**Can someone help me please I've tired this problem**

See similar problem here: http://www.jiskha.com/display.cgi?id=1481848396

**Data Probability**

See similar problem here: http://www.jiskha.com/display.cgi?id=1481848396

**algebra**

Factor x²-6x+9=64 x²-6x+9-64=0 x²-6x-55=0 the factors of 55 are 11 and 5 the difference of which is 6, so try (x-11)(x+5)=0, and it works. This the solutions of the equation are {11,-5} Check: (11^2-6*11+9=64, so 11 is good. Check the same for -5.

**Math**

Given: radius=7cm Circumference=perimeter of rectangle Ratio of breadth:length = 4:7 Let b=breadth, then length=(7/4)b circumference=2π(7)=14π circumference=perimeter therefore 14π=2(b+(7/4)b) 14&;i;=2(1+7/4)b (11/2)b=14π b=14π(5/11)=7.997=8 cm approx. Check: ...

**Geometry**

o 6 o o o 5 o 7 o o o 8 o The sum of the four angles equals 360°. ∠ 5= ∠ 7 (vertically opposite angles) Similarly ∠ 6= ∠ 8 (vertically opposite angles) Sum of the four angles ∠5+∠6+∠7+∠8=360° 2( 2x+15 + 3x) = 360° solve for x and ...

**Math(Scale Factors and Scale Diagrams)**

The game is 1/4 of the wanted size, so each of the dimensions of the wanted sized table is four times as big. For example, if he wanted a size twice as big (scale factor = 2), then the dimensions are 2*(9 1/4) × 2(4 15/16) = 18 1/2 × 9 7/8

**CALC**

Let f(x)=2x-tan(0.18x) the area required is given by integrating, ∫(2x-tan(0.18x))dx for x=1 to 5. How did you come up with a value of 9? Please show your work so we can help you correct the steps. As a rough estimate, we can see that f(1)=1.81 f(5)=8.74 And it is a ...

**Algebra, please help**

5x+3y=7 ...........(1) 3x-5y=-23 .........(2) We try to cancel/eliminate one of the variables. I choose to eliminate y. 25x+15y=35 ...........5*(1)....(1A) 9x-15y=-69 .........3*(2).....(2A) Add (1A)+(2A) 34x=-34 Solve for x. Substitute value of x into 1 and solve for y.

**Maths**

P=2950 (principal) i=0.081 per month (period=1 month) n=18 (periods) A=P(1+i)ni (accumulated value) Take out the calculator and calculate the value of A, value after 18 months.

**Physics**

We don't see the diagram, but assume that the cart is at the beginning of an uphill slope of angle θ with the horizontal. The problem comes to a matter of conservation of energy, since friction is neglected. Kinetic energy of the running boy KE= (1/2) mv²=(1/2)...

**Algebra 1B Radical expressions & data analysis**

I think you meant: #4 6/(√3 + 2) #5 y = 3√(6x + 42) #6 y = 2 √(3x + 4) - 5 #7 y = √(x+4) - 3 Note that a space does not imply parentheses, which are very important in mathematics. Read, for example: http://www.mathgoodies.com/lessons/vol7/...

**BIO PLEASE HELP!**

Try reading carefully the following link: http://www.microbeworld.org/types-of-microbes/protista

**Biology**

See your other post.

**Probability - marbles**

8 black and 7 green in urn (15 in all) 5 drawn with replacement. Probability that first one is green: P(1)=7/15 Probability that second one is green P(2)=7/15 (ball is replaced) ... P(5)=7/15 For all 5 steps to succeed, multiply together the individual probabilities P(all five...

**Math**

A number is rational when it can be expressed as a fraction of integers. For example, 24 is rational because 24=24/1=48/2... -3 is rational because -3 = -6/2 = -3/1 .... So see if you can figure out if -49 is rational.

**Physics**

height, h=135*16 cm = 21.6 m Time taken, t= 5 min 40 sec = 340 seconds mass, m= 63.9 kg g=9.81 m/s² (note that all values are in SI units) Work done, W = mgh J (joules) = 13540.2 J (multiply together m,g & h to get work done) Power = work done per second, so = W/t J/s =...

**algebra**

Cats have 4 legs. Budgies have 2 legs. Two ways to do it: 1. use algebra. C=no. of cats 3C=number of budgies total number of legs 4(C)+2(3C)=30 10C=30 C=30/10=3 So 3 cats and 9 budgies. Check: 3*4+9*2=30, checks. 2. by guessing We don't know how many of each, make a guess...

**ns**

This is spam.

**statistic**

Step 1 initially there are 20 students of which 6 have blue eyes. Probability of choosing the first with blue eyes is 6/20. Step 2 There are then 19 students left of which 9 have brown eyes. Then the probability of choosing a brown eyed student is 9/19. Since it is a two-step ...

**computer science**

pseudocode: x=input package name, x=1 for A, etc. n=input number of hours ... cost=0 if x=1 then cost=9.95+min(0,2*(n-10)) else if x=2 then cost=13.95+min(0,1*(n-20)) else if x=3 then cost=19.95 else print "incorrect package" endif print x, n, cost

**calculus**

Very cute problem. The answer is as cute! Look at the table shown in: http://prnt.sc/atvi6m f(x) and f'(x) are given on the third row! If you are in an exam, your teacher may not appreciate the "cute" answer. So let's work it out: f(x)=1/(1+(1/(1+(1/x)))) If ...

**friction & centripetal force**

Given: r=4.5 m angular velocity ω=2*π/7.2 rad/s =0.8727 rad/s When the cat is at position of 3 or 9 o'clock, the horizontal acceleration due to centripetal force is at its maximum. The centripetal acceleration is a=rω² The centrifugal force is F=ma=mr&...

**Math**

The logical solution is to take away 3 from 27 and divide by two to give the smaller number. Then add 3 to get the bigger number. Check by adding the two results to see if they add up to 27. If you have to use system of 2 linear equations, then let x=smaller number y=larger ...

**Finance**

Oops! Good catch! Thanks. Elcia, please go with Reiny's answer.

**Finance**

Use the mortgage formula: Future value = FV = 1000000 payment per period = P (to be found) rate of interest (per period) = i (0.06/12=0.005 per month) R = 1+i = integrated rate = 1.005 n = number of periods = (55-28)*12=324 then FV=P(1+R+R²+R³+....+Rn-1) =P(R^n-1)/(R...

**Math Help**

Yes, they are correct! I didn't notice you gave answers, sorry.

**Math Help**

For question one, you need to look at each number (of eight digits) which represents 8 campers. Any digit 0 or 1 represents out-of-state campers. Count how many of the 20 numbers contain at least two of 0 or 1. For example, the first number is 69531217 which means that there ...

**Math**

There are 360° in a whole turn (an hour). So 24 degrees is, by proportion, (24/360)=1/15 of an hour. Add this to 12:59 to get the time.

**One Math Problem**

See help above http://www.jiskha.com/display.cgi?id=1455846917 In fact, we are the ones to ask you for any thoughts!

**probability**

P(diamond)=13/52 P(king)=4/52 To select a diamond and THEN a king (with replacement) is then the product of the two above probabilities.

**Personal Finance**

Front end loading is the commission of a given percentage to be deducted from the total amount invested. Here the percentage is 5.25%. The total amount invested is $20000. The product of the two is the commission (front-end load). See definition of front-end loading: http://...

**MATH**

This system can be solved readily by elimination. You can eliminate y by adding the first equation to twice the second equation. Show us what you get!

**programming**

You need to find n^m where m is the sum of the digits of n. Step 1: Find the sum of digits of n. You could try the following algorithm, either inline or using a function (method): Let k=n m=0 do until k<=0 m+=k%10 k/=10 end do Step 2: Raise n to the mth power: result=1 k=m ...

**Physics**

Take moments about the fulcrum and equate to zero. Solve for F=effort. on the load side: force = 600N distance from fulcrum= 0.5 m On the effort side: force = F N distance from fulcrum= 1.5m - 0.5 m = 1 m. Moment equals force time distance from fulcrum, clockwise positive.

**Surveying**

We have a parabola, and the crown is 6 inches over a 30-foot width, i.e. 15' on each side of the crown. The elevation of the crown is 612.58, and on each side of the road the elevation is 612.58-0.5'=612.08. Taking x=0 at the crown, the equation of a parabola with the ...

**Calculus**

s(t)=t²-6t+5 is the position vector. For example, at time=0 hour, s(0)=5, so the person is 5 miles north of LA, etc. Velocity is the derivative of position with respect to time, namely, v(t)=s'(t)=2t-6 At time t=0, v(t)=-6, meaning he was cycling towards LA. ...

**physics**

So rocket never got propulsion after launch, becomes a projectile. u=92.0 m/s, θ=33° horizontal velocity (constant) ux=u cos(θ) Time to reach wall (in seconds) t1=26.0/ux seconds vertical initial velocity uy=u sin(θ) vertical height at time t sy(t)=uy*t-(...

**Physics**

To find the resultant, resolve forces into x (due east) and y (due north) components and add. Use a diagram to help you understand the angles.

**physic**

The largest value of A+B is when they act in the same direction, and the resultant is the sum of the magnitudes. The smallest value of A+B is when they act in opposite directions, and the resultant is the difference of the magnitudes.

**Physics**

Without the diagram, we're as lost as you are! Is the force F acting up the plane, or down the plane? Is the force F acting horizontally or along the plane?

**physics**

X-component=200*cos(60)+120cos(210) (positive due east) Y-component=200*sin(60)+120sin(210) (positive due north)

**Physics**

Air speed=195 m/s (westerly) Air velocity = 195 m/s (West=positive) wind speed = 53 m/s (easterly) wind velocity = -53 m/s Ground velocity = air velocity + wind velocity = 195-53 = 142 m/s Distance = +276 km = +276000 m Time required = Distance/velocity = 276000/142 s = 1944 s...

**Physics**

1 W/m² is defined as 120 dB. For every 10 dB higher, power is multiplied by 10 times. Inversely, for every 10 db lower, power is reduced (divided) by 10 times. For example, 100 db = (120-20) dB=1W/m²*10^-2 75 dB = (120-45) dB = 1W/m²*10^(-4.5)=10^(-4.5) W/m²...

**math**

Similarly, for the westward leg, 1 degree of longitude is approximately 111 km*cos(50°)=71.3 km Since plane was at 70°W, and flew westwards, the longitude would increase. Use an accurate value of radius of the earth, R, to replace the 111 km. Formula is R*π/180.

**Physics**

Use KE=(1/2)mv^2 GPE=mgh where m=mass of plane v=velocity h=height of plane assuming reference plane is ground level. g=9.81 m/s² Use consistent units.

**Physics please i really need help**

For the reaction time, distance = velocity * time = 23.7*0.427 = 10.12 m For the braking time, v²-u^sup2;=2aS v=0, u=23.7 m/s, a=-9 m/s^2, S=(v²-u^sup2;)/(2a) =-23.7^sup2/(2*(-9)) =32.21 m Stopping distance is the sum of the two distances.

**Physics**

Speed = circumference / time Circumference = 2πr = 2*π*5.8*10^10 m = 1.16π*10^11 m Time = 88days * 24h/day * 60min/h * 60sec/min =7603200 s Speed = distance /time = 1.16π*10^11 / 7603200 = 47930 m/s = 47.93 km/s

**physics**

Assuming that the wood block is fixed and stationary. (a) acceleration, a = (final vel. - initial vel) / time = (v-u)/t = (0-16 m/s) / 0.5 = -32 m/s² (b) average force = mass * acceleration = 0.020 kg * 32 m/s² = 0.64 newton (c) Distance, S = ut+(1/2)at² = 16*0....

**To Soso**

See http://www.jiskha.com/display.cgi?id=1454378710 Hope you realize the problem when you post the same problem too many times, ... and not checking answers before reposts!

**Geometry**

For the chord AB k=mXB 2k=mAX We will construct diameter CD such that X lies on CD. Now CX=9+7=16 cm, XD=9-7=2 cm Using the theorem of intersecting chords (AB and CD), we have 16*2=k(2k) Solve for k.

**Math**

Agree with Damon. The only 4 digit number for which 1. all digits are odd, 2. sum of last two digits equal 16 3. divisible by 13 are 7397, 9997, 7579 each of which does not satisfy the requirements 4. digits being distinct, 5. number is less than 3000. However, if the ...

**math**

Solve step by step. Given a 3-digit number. 1. If it is divisible by 5, it must end with a 0 or a 5. 2. If the number is odd, the last digit must be 5. 3. if product of digits is 15, the product of the two remaining digits must be 15/5=3, namely either 1,3 or 3,1. I.e. the ...

**physical science**

momentum=60000kg m/s mass = 2000 kg use relationship momentum=mass * velocity which can be solved for velocity: velocity=momentum/mass

**FRENCH ! (:**

Accents on any keyboard can be done as shown in the following link, for example, & e a c u t e ; stands for é (skip the spaces between & and ;) http://www.starr.net/is/type/htmlcodes.html Other comments: yesterday is hier (not heir). la police et l'ambulance _____ ...

**Math**

When we're dealing with consecutive numbers representing the sides of a triangle, the average of the perimeter (i.e. perimeter/3) is the middle number. Hence find the other two numbers.

**Behavioral Stat. Lab**

Where proprietary software is involved, you have a much better help from your instructor because not everyone here has access to minitab.

**Math**

Student needs to learn the position value of decimal numbers, and that a carry should not shift the digits to the right.

**Phiysics**

use final velocity = initial velocity + acceleration * time Note: deceleration is a negative acceleration.

**math - typo?**

Do you mean: "You need 210 snowballs to make the perfect snow fort you make 15 snowballs in an hour but 10 melt every 15 minutes how long will it take you to make the perfect amount?" Checking your question before you post helps you get your answer fast.

**Math**

If AB is the longest side, then O cannot divide AC and BD in the ratio 1:2 since mAB>mDC. We will use A(BOC) to represent the area of triangle BOC, and so on. Draw a diagram of the trapezoid ABCD with AB//DC and AB>DC. The diagonals AC and BD meet at O. If the division ...

**science**

In the case of a hydraulic lift, the pressure is (almost) identical, so that Force/area is a constant, where area is the area of the respective piston.

**Science**

The keyword here is energy reserves. All except one provide energy, but under different conditions. Discover about all four at the link: http://www.livestrong.com/article/281655-functions-of-lipids-carbohydrates-nucleic-acids-proteins/

**Science**

Ethyl alcohol has a formula of C2H5OH. C8H18 is octane. In any case, you would work out the number of moles of alcohol in 16.5 mL. (note: 16.5 mL*0.789=13.02g) Each mole of alcohol gives out 2 moles of CO2. (Write out the combustion equation). So by proportion, you will get ...

**MAth 10 (probability**

Make a table for the two spins X| 1 2 3 4 --------- 1| 2 3 4 5 2| 3 4 5 6 3| 4 5 6 7 4| 5 6 7 8 Out of the 16 possible outcomes, count how many satisfy the given condition, and divide this number by the number of possible outcomes.

**Math**

We'll first find the limit, and I'll let you continue with the derivative. Let Y=Lim x->∞ (2^x+5^x)^(1/x) =Lim x->∞ ((5*2/5)^x+5^x)^(1/x) =Lim x->∞ ((5^x)(2/5)^x+5^x)^(1/x) [law of exponents] =Lim x->∞ ((5^x)((2/5)^x+1)^(1/x) [...

**Chemistry-Dr.Bob**

Correction: the answer is more appropriately given as 1.54 J/(g-°C) as all the original information is given to 3 significant figures.

**Chemistry-Dr.Bob**

Use ΣmcΔT=0. For metal, mcΔT=100*c*(29-90)=6100c For water, mcΔT=250*4.184*(29-20)=9414 Applying ΣΔT=0 => 100*c*(29-90)=250*4.184*(29-20) Solving for c gives 1.543 J-g-1-°C-1 as you had it.

**math**

It depends on the given information. If base radius (r) and height (h) are given, then angle of cone is given as 2tan-1r/h.

**math**

the parabola y=x² has it's vertex at (0,0). Tangent to parabola has slope dy/dx=2x, at point (±x, x²). For tangents to pass through (0,-25), we have the slope joining (0,-25) and (x,x²) equal to 2x. Slope=(y2-y1)/(x2-x1) => (x^2-(-25))/(x-0)=dy/dx=2x ...

**French**

There is not enough context to give an answer without making assumptions. However, if we assume this is an itinerary for Élaine, the second date (8 days later) could be assumed to be the return (to San Diego) from Marseille, which is reasonable for a tourist. Assuming ...

**physics**

It would appear as homework dumping if you don't show your work. Also, if you make an effort to solve the first one, there is a chance you can apply what you learned to solve the other ones, or at least get a good kick-start. I suggest you review class material, attempt ...

**Maths**

The best way to include a picture is to upload the picture to an image server and post the link. It is not always possible, but give it a try and teachers are likely to help you get it done if there are difficulties.