Saturday
April 18, 2015

Posts by MathMate


Total # Posts: 11,238

chemistry
molar mass of CH3COOH =(12+3+12+16+16+1) =60 mass of acetic acid in 250 mL of 0.26M =(250/1000) L * 0.26*60 = 3.9 g
April 15, 2015

More math
9C4=9!/((9-4)!4!) Use your calculator to work that out.
April 15, 2015

Math
nPr=n!/(n-r)! 6P2 =6!/((6-2)!) =?
April 15, 2015

Simple math.
n! = n(n-1)(n-2)...(3)(2)(1) for example, 3! = 3*2*1=6 You can use the ! or factorial function of your calculator to find the answer for 5!. You can also calculate the products long-hand.
April 15, 2015

maths
clarification: Hint: DC is not parallel to AB unless ∠DAB is 90°.
April 15, 2015

maths
It is an excellent exercise to follow instructions in order to draw a diagram. I would let you do just that, and at any step the statement is incorrect, it is the required answer. Hint: DC is not parallel to AB.
April 15, 2015

physics - good catch!
Haha! At least someone noticed that! Yes, in my days, slide-rules were not accurate enough, and survey calculations were done using 7-figure (log and trig) tables which were packed in a volume (I still have one!) thicker than today's calculus textbook. That taught me how ...
April 15, 2015

basic trigonometry
I hope you mean the ski track along the mountain is 235 m long. The mountain can be represented by a right triangle with the two legs horizontal and vertical, and where the angle of elevation is 35°. The ski track is the hypotenuse (C), and if the horizontal leg (B) and ...
April 15, 2015

math-need figure
To ollie: The question is meaningless without the accompanying diagram. You could post a link to the diagram, or you can describe what the diagram looks like. Sorry that we cannot go further without the rest of the required information.
April 15, 2015

linear algebra
Use the properties of linear transformations: 1. T(A+B)=T(A)+T(B) 2. T(kA)=kT(A) then let A=[1,1], B=[-1,1] and T(A+B)=T(0,2)=[-2,1]+[3,2]=[1,3] => T(0,1)=[1/2, 3/2]=P and T(A-B)=T(2,0)=[-2,1]-[3,2]=[-5,-1] => T(1,0)=[-5/2, -1/2]=Q So (a) L(-1,5)=-P+5Q =-[1/2,3/2]+5[-5/2...
April 15, 2015

statistics
7 choose 5 = 7C5 = 7!/((7-5)!5!) = ? ! means factorial.
April 15, 2015

statistics
probability is constant and independent of trials. trials are Bernouli, i.e. either success or failure. Number of trials is known. All this point to the binomial distribution where P(k successes out of n) =nCk p^k (1-p)^(n-k) p=probability of success of each independent trial=...
April 15, 2015

physics
Solve for n in PV=nRT 2.79*10^5(3.66)=n×8.314462175×(19.8+273.15) to get 419 moles (3 sig. figures) and similarly solve for P in P(7.20)=419.235(8.314462175)(28.5+273.15) to get 1.46*10^5 (3 sig. figures) Your approach is correct, but cannot tell where you got ...
April 14, 2015

physics
131 m. :)
April 14, 2015

Mechanical Principles
corrections. I forgot to multiply F(x) by x in the integral. So T should read less than 6 kN instead of 10.
April 13, 2015

Mechanical Principles
We have an increasing hydrostatic pressure varing from zero at water surface to the depth of the water, which exerts a varying force on the gate. The tension on the cable can be obtained by taking moments about the hinge of the gate (at the bottom). Let H=height of gate (where...
April 13, 2015

CIRCUITS
Resistance across resistors in series = R1+R2+R3 Voltage across each resistor is proportional to the fraction of each over the total. For example, resistors R1=2,R2=1,R3=3, ohms are connected in series and subject to a voltage of 12 volts, Resistance of resistors in series R=...
April 12, 2015

Math
For a rectangle, area = length × width perimeter = 2(length + width). Example: for a rectangle with length = 5 ft width = 3 ft area = 5×3 = 15 square feet perimeter = 2(5+3) = 16 feet
April 12, 2015

maths
Volume of a cube, Vc = (side length)³ Volume of a cylinder Vcy= πr²*h where h=length/height of cylinder r = radius of base = diameter of base /2 If their volumes are equal, then Vcy = Vc πr²*h = side³ Solve for h.
April 11, 2015

geometry
Height / distance = tangent so distance = height / tangent = 28 ft / tan(11°) = ...
April 10, 2015

maths
SI=simple interest formula is Interest = Principal * annual interest rate * number of years = 225 * 0.16 * 3.75 = 135 Add interest to principal to get final repayment amount.
April 10, 2015

Combinations-Math
74 is correct.
April 10, 2015

physics. urgent answer please
F1=10 N at 60° F2=15 N at 0° Use x- and y-components method: x-component Fx=F1*cos(60)+F2*cos(0) =20 N y-component Fy=F1*sin(60)+F2*sin(0) =8.660254 N Resultant, R= √(Fx²+Fy²) angle, θ = atan2(Fy, Fx) Hints for checking your answer: 20 N < R &...
April 10, 2015

French
The words are in the right places and the right form, except for #2 where the number does not agree with the definite article "le". It should be either l'assiette (sing., more probable) or les assiettes (plur.) Not knowing the instructions nor the purpose of the ...
April 9, 2015

linear algebra urgent
http://www.jiskha.com/display.cgi?id=1428173198 Also, remember that u3=u3-p(u1,w3)-p(u2,w3) where p(u1,w3) is the projection of w3 on u1, etc.
April 9, 2015

linear algebra urgent
see other post
April 9, 2015

Math
Assuming that strawberry on vanilla is considered the same flavour as vanilla on strawberry, i.e. order of the two scoops doesn't count, then there are 30C2 possible flavours, and 3 cones for a total of n=3(30C2) possible ice creams. For an order of 12 different ice-creams...
April 9, 2015

math
If you could post the question exactly as you were given, it would be possible for us to understand what you need. Especially in math, paraphrasing tends to lose important information.
April 9, 2015

maths
If the GP has its third term as 9 times its first term, then the sequence is a, ar, ar² where a is the first term, ar is the second term, etc. This means that ar²/a = r²=9, or r=3. Similarly, the fifth term divided by the second term should be a^4/a^1 = a^3, or ...
April 9, 2015

Math
The quadratic formula assume the equation to be: ax²+bx+c=0 (i.e. all terms are on the left-side of the equation). Rearrange the equation to be 3x²+4x-6=0 and try again. You do not need a graphing calculator to find the zeroes. Either by hand, or a regular calculator...
April 9, 2015

Trigonometry (identities) (last help needed)
Typically with simplification like these, you would convert all functions into sine and cosine, and simplify from there on. Use sin²x+cos²x=1 whenever appropriate.
April 9, 2015

Trigonometry (identities ?)
Trigonometric identities involve an equal sign with a different expressions on either side. So it's not clear what exactly you require in your questions. Do you need to simplify the expressions? I suggest you check for typos as well as I do not see what β has to do ...
April 9, 2015

linear
To find W⊥, you can use the Gram-Schmidt process using the usual inner-product and the given 5 independent set of vectors. Define projection of v on u as p(u,v)=u*(u.v)/(u.u) we need to proceed and determine u1...u5 as: u1=w1 u2=w2-p(u1,w2) u3=w3-p(u1,w3)-p(u2,w3) u4=w4-...
April 9, 2015

CALCULUS
f(x)=9x³-4x^5 F(x)=∫f(x)dx=(9/4)x^4-(4/6)x^6+C Given F(1)=0, solve for C and hence find F(4) F(1)=(9/4)1^4-(4/6)1^6+C=0 => C=(4/6)-9/4=(8-27)/12=-19/12 => F(x)=(9/4)x^4-(4/6)x^6-19/12 Find F(4)
April 9, 2015

Math (Help please)
Rows are horizontal, numbered from top to bottom, columns are vertical, numbered from left to right. For example, element at row 1 column 3 is equal to 6, element at row 2 column 4 is equal to 0.
April 9, 2015

physics - work, power
We do not support LaTeX here, but you can use / for division, and unicode symbols for special characters. Power = work / time work = Force * distance speed = distance / time force * speed = force * distance / time I believe the four equivalences are sufficient for you to get ...
April 9, 2015

READ - to Sarah
Well said! Thank you!
April 9, 2015

Physics
Mass of water that escapes per unit time = m Since the mass of water drops in height by an equivalent of h=1.14 m, we can equate change in energy = 0, or mgh-(1/2)mv^2=0 Solve for v
April 9, 2015

Physic
Power for resistors in series = V²/(R1+R2) Power for resistors in parallel = V²/(1/(1/R1+1/R2)) = V²*(1/R1+1/R2) Solve for R2.
April 9, 2015

Physic
Power = V²/r watts so resistance for the 75W bulb R1 = 120²/75 Ω = 192 Ω Similarly calculate R2 for the 25W bulb. Net resistance of two resistors in parallel R = 1/(1/R1+1/R2)
April 9, 2015

physics
Without air resistance, time to drop to ground (irrespective of horizontal velocity) t = √(2gh) horizontal distance = horiz. velocity * t
April 9, 2015

Mechnical principles
Archimedes principle: Buoyant force on a submerged or floating object is equal to the weight of fluid displaced. Volume of metal = volume of fluid displaced = weight of fluid displaced / density of fluid = (buoyant force) / density of fluid = (500-446) g / 1000 g/L = 54 mL ...
April 9, 2015

Math.
1-4 are correct. For #5, interest = 1200*0.045*2=108 principal = 1200 Total to repay = 1200+108=1308.
April 9, 2015

Math help
Yes, B is correct, here's how: 3.36/6=(3+0.3+0.06)/6=3.00/6+0.30/6+0.06/6
April 8, 2015

mat
4.5% compounded monthly is i=0.045/12=0.00375 per month. n=38 months Present value, Pv=125 Future value, Fv = Pv(1+i)^n
April 8, 2015

statistics
4***5***6***7***8***9***10 If your studying time is a total of 6 hours between 4 and 10 pm. Time left after 8 pm is 2 hours. Assuming random checking, probability that study time after 8 would be the time period between 8 and 10 divided by the total possible time from 4 to 10.
April 8, 2015

math-permutation
The four digits are distinct, so there are 4! possible permutations of the digits.
April 8, 2015

algebra
I have not checked or proved, but believe (6,8,10) is the only triplet that is consecutive even. If you would like to search for more triplets, here's a reference to the work of Brahmagupta: "Pythagorean triples[edit] In chapter twelve of his Brahmasphutasiddhanta, ...
April 8, 2015

Physics !
A. you get the idea, but results can be simplified further Since the bulbs are identical each with resistance r, then in series, R=3r, in parallel, 1/R=(1/r+1/r+1/r)=3/r, in other words, R=r/3. B. Current = i, governed by V=iR. For light bulbs in household circuit, V is ...
April 7, 2015

math
Let x=number of mystery books on the shelf then 3x = total number of books on the shelf we are told that x/5<10<x/4 multiply by 20, 4x<200<5x which means that 40<x<50 So the number of mystery books can be any number between 41 and 49. In other words, the ...
April 7, 2015

physics
Energy = mgh h=difference in elevations between floors. The number of steps is irrelevant because it's the total difference in elevations that counts. If m is in kg, g in m/s², and h in metres, the result mgh is in joules.
April 7, 2015

MATH PLZ SOMEONE HELP
Bread costs $2 a loaf. How much would 1 loaf cost? How much would 2 loaves cost? How much would 10 loaves cost? etc. Similarly, Babysit earns $10 an hour. How much for 2 hours? How much for 5 hours? How much for 10 hours? How much for h hours?
April 7, 2015

Physics - impressive
Your posting speed is impressive, at less than 20 second interval for 7 posts. However, your efforts in solving problems is at the other extreme. The more effort you show, the more chance that help will be given in priority. In fact, you are encouraged to post a problem, study...
April 7, 2015

Physics
(a) Total tension = tension due to mass + tension due to acceleration = mg + ma (b) tension at uniform velocity = tension due to mass only = mg
April 7, 2015

Astronomy
It turns out that detecting planets around other stars is by the periodic dimming of the star, caused by the "eclipse" of the star by the planet. A smaller planet will dim the star to a lesser extent, hence either the periodic dimming phenomenon is more difficult to ...
April 7, 2015

NEED HELP PHYSICS!!!
Equate the centripetal force to 6.8g, i.e. mv²r = 6.8mg solve for r. Note that mass of aeroplane cancels out.
April 7, 2015

NEED HELP PHYSICS!!!
At the bottom of the swing, the vine is subject to two forces, gravity force = mg centripetal force = mv^sup2;/r m=mass of Tarzan (kg) g=acceleration due to gravity (9.81 m/s²) v=tangential velocity (m/s) r=radius of circular motion =length of vine (m) At point of rupture...
April 7, 2015

NEED HELP PHYSICS!!!
Centripetal force is the force that maintains an object in a circular motion. This is an external force that acts on the object in the direction of the centre of the circular motion, namely tension of the string in this case. Centripetal force may be calculated using the ...
April 7, 2015

math
By the pigeon hole principle (where each hole houses one car), it is impossible to have 23+34=57 repairs in 50 lifts (cars). So the surplus must go to cars that need both repairs. This is the least number of cars that need both repairs. Assuming that all cars need at least one...
April 7, 2015

physics
v²-u²=2aS v=0 u=-7.5 m/s S=-4.2 m Solve for a=acceleration in m/s² a=7.5²/(-2×4.2) =6.7 m/s²
April 6, 2015

Math
Median is the middle number of a sorted list of data such that there are as many numbers above it as there are below. For example, median of the set of numbers {3,5,7,10,14,18} is 8.5, which is the average of the two middle numbers. The median of {1,4,9,13,16} would be 9, ...
April 6, 2015

French
"adorer" is a transitive verb (meaning it requires a direct object). Based on Missy literal translation can you correct the sentence? Alternatively, you can say simply J'adore ... the warm days....
April 6, 2015

French (if correct translation/grammer)
Indeed, Ms Sue is right. To clarify, could you tell us if the objective of the exercise is to write a literary essay, or is it a translation exercise? In either case, it would be much easier if you would give the original English version, seeing that the text shows evidence of...
April 6, 2015

Physics
The second parachutist must open the parachute at the moment that she catches up with the first, i.e. has fallen the same distance as the first. 1. Establish the time/distance relation of first parachutist. For the first 3 seconds, distance = 0 + 9.8*(3²) = 44.1 m total ...
April 6, 2015

physics
1 revolution=2π radians 1 minute = 60 seconds (a) Angular acceleration = 180 rpm/8 s =22.5 rpm / s = 22.5*(2π) radians/60s /s =3π/4 rad/s² (b) No. of revolutions =average angular speed * time =(0+180)/2 rpm * (8/60) min = 12 revolutions
April 6, 2015

physics
Power = work done / time Work done =mgh =50*9.8*250 =122500 J Time =10*60 s =600 s Power = work done /time =122500/600 J/s = 204.2 W
April 6, 2015

physics
If car is accelerating uniformly, after 10 seconds, the velocity is 30/2=15 m/s. Distance travelled is time * average velocity =10 s × (0+15)/2 = 75 m Or calculate average acceleration a=30 m/s / 20 s =1.5 m/s² Distance =vi t + (1/2) a t² =0(10)+(1/2)(1.5)(10&...
April 6, 2015

Telecommunication 2.
Radio waves are electromagnetic waves and obey the relation v=fλ f=frequency (Hz) λ=wavelength (m.) v=velocity, m/s and in vacuum,equals the speed of light for electromagnetic waves c=3×108 m/s in air, v is slightly less than c. So solve for f in the above ...
April 6, 2015

physics
"KE 1= 1/2*0.002kg*300^2m/s=30 j KE2=0 work " should result in 90 J (and not 30 J), and assuming energy dissipation is uniform, then KE=W=F*d, F=KE/d=90/.05=1800 N which is exactly the answer you got for the second part. Note: units which are proper names (pascals, ...
April 5, 2015

physics
Correct, well-done! :)
April 5, 2015

Chemistry - Stoichiometry
From the equation, find the stoichiometric ratio of HCl and MnCl2 which equals 2. This means that 1 mol of MnCl2 will generate 2 mol of HCl. Using the fact that 1 mol of HCl occupies 22.4 L at STP, you will find how many mol of MnCl2 will be required to make 0.054 L of HCl.
April 5, 2015

maths - cosine rule
Use the cosine rule: c²=a²+b²-2ab cos(C) with a=7, b=15, and included angle C would vary from 0 to 180 degrees. Note that these limits themselves are not valid values, i.e. max>c>min. They represent the sum and difference of the two sides.
April 5, 2015

Math
An equation of a line must include an equal sign, and your answer does not have one. You probably meant y=-4x+10 Recall some properties of a dilation includes 1. conservation of parallelism, ------------------------------ i.e. lines before and after dilation should remain ...
April 4, 2015

math
Almost. It's 800 cubic feet. Units are important in the answers.
April 4, 2015

math
(2, 2 square root 2, and 2 square root 3) means (2, 2√2, 2√3) Square each number: (4, 2²×2, 2²×3) =(4,8,12) Do these numbers make a Pythagorean triplet?
April 4, 2015

geometry
See your later post.
April 4, 2015

linear algebra check
You have u1 and u2 correct. Don't know if you're expected to rationalize the denominator, in which case, u1 would read [(√3)/3,(√3)/3,(√3)/3]...etc. u3 should be [0,....] A good way to check your answer is to verify if u1.u2=0, u1.u3=0, u2.u3=0.
April 4, 2015

Chemistry
Keq can be obtained by substitution of the product concentrations and reactant concentrations in the definition of Keq. If in doubt, read: http://www.horton.ednet.ns.ca/staff/jeffrey/Chem%2012/answerkeysMJeffrey/kineticsandrates/Meaning%20of%20Keq%20page%201.pdf or examples in...
April 4, 2015

accounting
You can solve using the compound interest formula: Fv = Pv * (1+i)^n Fv=future value, to be calculated Pv=Present value ($8000) i=interest per period (6%/2=0.03) n=number of periods (2)
April 3, 2015

chemistry ap
Assuming zinc is in excess. 18 mL of 6.00 M H2SO4 equals 0.108 mol From Zn+H2SO4 -> ZnSO4 + H2 we deduce that 1 mol of H2SO4 produces 1 mol of ZnSO4. So mass of ZnSO4 produced is 0.108 mol, multiplied by the molecular mass of ZnSO4.
April 3, 2015

accounting
Use compound interest formula: Fv=Pv(1+i)^n here Fv=7500 Pv=present value to be calculated i=8%=0.08 (assume compounding annually) n=18 transposing, Pv=Fv/(1+i)^n
April 3, 2015

math discrete
Oops, I didn't do what the question asked. Go with Reiny's solution!
April 3, 2015

math discrete
f(x)=4x³ g(x)=2x h(x)=x² h◦(g◦f) =h◦(g(x²)) =h◦(2(x²)) =h◦(2x²) =4(2x²)³-5 =4(2²x²)³;-5 =4(2^6 x^6)-5 =256x^6-5
April 3, 2015

PHYSICS
You can read the response to the previous post and try to work out the answer.
April 3, 2015

PHYSICS
By the law of floatation, any floating object will displace a mass of fluid equal to its own mass. So a floating object of volume 1 m³ density 400 kg/m³ will displace 400 kg of water, i.e. fraction of immersed object is 0.4, equal to its specific gravity, and ...
April 3, 2015

math - typo?
A cubic foot of water weighs 62.4 pounds. An imperial gallon of water weighs 10 pounds. You used kg all over, so it is not clear whether there is one or more typos in the question. You will need to check the question and make appropriate corrections before your answer can be ...
April 3, 2015

math
First possibility: 10 B = 10 B After that, we can take advantage that 3B weighs as much as 2A, so you can progressive change every 3B for 2A, for example, 7B+2A = 10B 4B+4A = 10B there is one more that I will leave you to finish.
April 2, 2015

Math
All correct except the first: The square of the length ...
April 2, 2015

math
5•4•3 does not equal 40, you probably meant 5*4*2 you can add 5*8*1 If order does not count, I don't see other ways.
April 2, 2015

calc
A vector that is orthogonal to two given vectors is the cross product, namely |i j k| |x1 y1 z1| |x2 y2 z2| which in this case is |i j k| |1 6 1| |1 -9 1| Expanding the determinant, we get the following vector: <6*1+1*9, 1*1-1*1, 1*-9-6*1> <15, 0, -15> which can be...
April 2, 2015

biology
Some cons to think about: 1. Mandatory donation will no longer be a donation, it will be an obligation. 2. What do you think about the individual rights of citizens of Canada. 3. The need may be urgent, but will the organs of ALL Canadians be required?
April 1, 2015

7TH MATH HELP
A translation is defined as: T: (x,y) -> (x+p,y+q) where p and q are given constants. For example: (10,3) -> (10+p, 3+q) = (1,6) 10+p=1 => p=1-10=-9 3+q=6 => q=6-3=3 So we have established that the translation is T: (x,y) -> (x-9, y+3) (note: if p is positive, ...
April 1, 2015

Algebra 2
Expand sin2θ = 2sinθcosθ so sin2θ=-cosθ 2sinθcosθ + cosθ = 0 factoring out cosθ, cosθ(2sinθ+1)=0 cosθ(sinθ+1/2)=0 Using the zero product property, we deduce that cosθ =0 OR sin&theta=-1/2 Solve...
April 1, 2015

Exponential Equations
Direct substitution of equation: Pv=present value Fv=future value Fv=Pv*(1+i)n where i=interest rate per compounding period (assumed year here) n=number of compounding periods (assumed year here). note that 2.75% is equivalent to 0.0275 for i (interest rate). If both Pv and Fv...
April 1, 2015

Physics
The difference of 2.5 minutes per day is assumed to be due to the difference in g at the two locations. If in Cayenne it loses 2.5 minutes per day, it means the period there is longer. To find how g affects the period, we are given the relationship T=k/sqrt(g) where k is a ...
April 1, 2015

precalculus
If you're not getting the correct answer, I suggest you post how you got your incorrect answer so that we will help you find what went wrong. This is the whole purpose of solving problems.
March 31, 2015

chemistry to MathMate
In case you got confused with the units, I underline that the units are the same, namely, nanometre, or nm. You have a tube of length of 5000 nm, and diameter of 1 nm. How many time is the length bigger than the diameter?
March 31, 2015

chemistry to MathMate
5000 nm is correct. How many times as big is 5000 nm (length of tube) compared to 1 nm (diameter of tube)?
March 31, 2015

to CJ
Perhaps it is easier if we go back to the question to make sure we understand information given in the question, and what the question is asking. "Nanotubes are rolled up cylinders of graphite with diameters of about 1nanometer, and lengths in micrometers." The above...
March 31, 2015

links to previous posts
For reference, these are the links to related posts on the same question. http://www.jiskha.com/display.cgi?id=1427844366 http://www.jiskha.com/display.cgi?id=1427822942
March 31, 2015

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