Thursday
December 8, 2016

Posts by MathMate

Total # Posts: 11,499

Math
A dart board has sectors numebered from 1 to 20. We require combinations, so order does not count. Here's how we could proceed: 1. to avoid repetitions, we assume the smallest number is thrown first, then the next smallest, and the largest numeber. 2. There are no limit to...
January 5, 2016

Counting and Probability
Let k=number of 4's to add then E(x)=Σx*P(x) =(8*2+(2+k)*4)/(8+2+k) If E(x)≥3.5 then (8*2+(2+k)*4)/(8+2+k)≥3.5 solve by cross multiplication 16+8+4k≥35+3.5k 0.5k≥11 k≥22
January 5, 2016

partial fraction
step 1: decompose denominator into factors (x³_x²-x-1) =x²(x+1)-1(x+1) =(x²-1)(x+1) =(x+1)²(x-1) Now decompose expression into partial fractions: (Ax+B)/(x+1)² + C/(x-1) = (2x²+7x-1)/(x+1)²(x-1) .....(1) Now match coefficients of powers ...
January 5, 2016

math
What's left is is 100-80=20% So the original amount A can be found by proportions: P100/20%=X/100% solve for X: P100*100%/20%=P500
January 5, 2016

french(le passe compose)
To help you better, I suggest you propose your translation and we will be glad to help you make necessary corrections. For example, (for a male speaker) "I went to school yesterday" would be Je suis allé à l'école hier. Recall that in French...
January 5, 2016

Physics
Hint: read up about Newton's first law, for example, at the following link: http://www.physicsclassroom.com/class/newtlaws/Lesson-1/Newton-s-First-Law
January 4, 2016

physics
Inelastic collision means the two objects do not rebound and move at a common velocity. Yes, choice a is correct.
January 4, 2016

math
*...is related to sign of...
January 3, 2016

math
monotonicity of ln(x) is equal to sign of (ln(x))'=1/x, and domain of ln(x) is D=(0,+∞) Since 1/x is strictly positive for x∈D, so ln(x) is strictly monotonically increasing.
January 3, 2016

physics...perhaps horizontal plane
I assume that the block of mass m=80 kg slides horizontally, and that the force F=400N pushes downwards at an angle of θ=37° below the horizontal. Initial horizontal velocity is u=20 m/s, and we look for velocity v at time t=6 seconds. Further assumption: friction &...
January 3, 2016

Math - typo?
The question as is would provide 3 equations for two unknowns. It would be a good idea to check the question before/after posting.
January 1, 2016

MATHS HELP URGENT(TIME AND WORK)
Fraction of work accomplished W at the end of day t will be denoted W(t). W(0)=0 W(10)=5/6 W(12)=5/6-2/3=1/6 W(22)=1/6+5/6=1 work completed.
January 1, 2016

math
Hint: adjacent angles of parallelgrams are supplementary, i.e. they add up to 180°. For the given problem, if one angle is x, then the adjacent angle is 2x. Since they are supplementary, we have x+2x=180°. Solve for x and hence the angles of the parallelogram.
January 1, 2016

dynamics
Let time t=0 when mass is 3500 and speed is 1220 m/s. then F(t)=500 kN m(t)=3500-80t a(t)=(500*1000/m(t))=acceleration => (i) v(10)=v(0)+∫(500000/(3500-80t))dt for t=0 to 10. =1220-500000[ln(3500-80t)]/80 =1220+1621.945 =2841.945 m/s (ii) using initial mass v(10)=v(0)+(...
December 29, 2015

Math
In four years, the total of the ages will be 46+4+4=54 years. The ratio in four years will be 7:2 So age of daughter in four years = 54*(2/(7+2))=12 age of mother in four years = 54*(7/(7+2))=42 Continue to find their present ages.
December 28, 2015

chem question?answer_to=1210023143
(115 psi)/(14.7 psi/atm) = 7.82 atm assuming the air in the tire has room temperature.
December 28, 2015

physics
Assuming the 10N force is along the positive x-axis. Then the three forces in (magnitude, angle °) are P(10,0), Q(30,120), R(50,240) or in component form: P<10,0> Q<30cos(120),30sin(120)>=<-15, 25.9808> R<50cos(240),50cos(240)>=<-25, -43.301> ...
December 28, 2015

mathematics
Assuming parentheses around the denominator have been omitted, the expression is x²+x+4/[(1-x)(x²+1)] partial fractions for the third term is required, namely 4/[(1-x)(x²+1)] =-4/[(x-1)(x²+1)] =A/(x-1)+(Bx+C)/(x²+1) By adding the right-hand side, we ...
December 28, 2015

Algebra
Constraints: A. x≥0 B. y≥0 C. y-x≤100 D. x+2y≤1400 (please check this constraint) Draw the graph of the constraint equation to have a visual understanding. Solve for all possible corners of the feasible polygon. Note that all inequalities are inclusive, i.e. all ...
December 27, 2015

Math
We know that 5*7=35, so the three digit number probably starts with a 3, and the two digit number starts with a 7. We also know that we should put small digit after 7, and large digits after 3, so the numbers are 384/71 Check: 5 < 384/71=5.408 < 6 There may be other ...
December 26, 2015

stats
Good catch Reiny! I read too fast! To "Help", please go along with Reiny's answer.
December 23, 2015

stats
Yes, that would be correct, because 10+20+30+40=100 so the the probability that she selected French hens would be 10/100.
December 23, 2015

stats
There are 10 French hens. Try to enumerate the number of each kind of pet and then add up the numbers to get the total number of pets. 40 is the number of American chickens.
December 23, 2015

stats
Let success be choosing a French hen out of all possible choices (Ω) and we need to assume the probability of choosing any pet is equal. Probability of success (choosing a French hen) =Number of French hens ÷ Total number of possible choices (&Omega). Here you see...
December 23, 2015

Physics
Assuming uniform deceleration and constant friction (independent of speed). Equate energies: (1/2)mu²=μmgX X=distance u=30 m/s g=9.81 m/s² Solve for X=61.1621 m Acceleration v²-u²=2aX solve for a=(0²-30²)/(2*61.1621) =-7.3575 m/s²
December 22, 2015

statistics
The requirements for an experiment's to be considered binomial are: 1. probability of success remains constant throughout the experiment 2. all trials are independent and random 3. the number of trial is constant and known. This problem satisfies the requirements for the ...
December 21, 2015

Calculus
Distinguish between relative maximum and absolute maximum. Statement (a) is true for absolute maximum since x0 is where f(x) has the highest value over the domain of f. Relative maximum at x0 only guarantees that f(x0)>f(x0-) and f(x0)>f(x0+), i.e. a local maximum.
December 21, 2015

Physics
Work to transformed water to steam = 4*10^8 J Work to overcome safety valve=2*10^8 J. Both work are added to the internal energy.
December 21, 2015

To Paige -- French
Also a version with the accents.
December 21, 2015

French
Here a version with the accents filled in. Good luck! Vous avez besoin de: -1 c. à s. de l’huile -200 g du riz -2 oeufs -3 tranches de fromage -300 g de haricots noirs -2 tomates -1 oignon -1 c. à s. des épices mexicains -2 gousses d’ail -(...
December 20, 2015

physics
M1. The direction of the initial velocity of 3.5 m/s is not mentioned. Use S=ut+(1/2)at^2 to solve for time t. S=-100m (distance) a=acceleration due to gravity = -9.81 m/s^2 u=initial velocity u=0 if 3.5 m is horizontal u=-3.5 if he dove into the ocean at that velocity.
December 20, 2015

Counting and Probability
These are very interesting problems. If you show some efforts in solving them, there would be likely to be more chances of response.
December 16, 2015

gss
A'BC+AB'C'+A'BC+ABC+AB'C =(A'BC+ABC)+(AB'C'+AB'C)+A'BC =(BC)+(AB')+A'BC =(BC+A'BC)+AB' =BC+AB'
December 16, 2015

Algebra 2
see http://www.jiskha.com/display.cgi?id=1450209752
December 15, 2015

algebra?
Hint: the ratio is 2:3, so from A to B, it is 2/(2+3)=2/5. The coordinates of M are: M(xa+(xb-xa)*2/5, ya+(yb-ya)*2/5)
December 15, 2015

Algebra 2
x-intercept is obtained by solving for x after setting y=0. For example: f(x)=x^2+2x+1 set y=f(x)=0, then x^2+2x+1=0 (x+1)²=0 x=-1 (x-intercept) y-intercept is obtained by solving for y after setting x= 0. For example : f(x)=x^2+2x+1 Set x=0, then f(x)=y=0^2+2(0)+1=1 y=1 ...
December 15, 2015

Numerical Analysis MATLAB
Hint: http://www.mathworks.com/help/matlab/ref/fplot.html
December 15, 2015

Math - ratios
Let N=number of papers graded in 1.5 hours (90 minutes). Use ratio (assuming the grading rate is constant) 5 papers: 45 minutes = N papers : 90 minutes. Cross multiply: N=(5/45)*90=10 papers.
December 14, 2015

math
There are two ways to solve this problem. A. The intuitive (and fast) approximation is by prorating the ratio, assuming that the ratio is constant. Let N=total population, then N/30=20/4 => N=150 B. The more accurate (and elaborate) way is to use the hypergeometric ...
December 14, 2015

Math
Let x=cost of pizza. then 3x/8+4=5x/8+1.5 solve for x.
December 14, 2015

math-legs and heads, again
See response at http://www.jiskha.com/display.cgi?id=1450138210
December 14, 2015

math-legs and heads
You can choose to do the sum mentally as follows: If all the animals were ducks, there would be 2*22=44 legs. Since there are (60-44)=16 more legs, there must be (16/2)=8 dogs, the rest (22-6)=14 ducks. If you prefer to solve the sum mathematically, you would set up an ...
December 14, 2015

Math
Since the area is bounded by two parallel lines y=5 and y=-3, the area is a trapezoid, with a height of (5-(-3))=8. We need to find the intersection of the line y=2x-5 with each of the parallel lines. Setting 5=2x-5 => x=5 Setting -3=2x-5 => x=1 So the upper width is (8-...
December 14, 2015

Mathematics
(2+x)(-sinx) is an expression, and cannot be solved. To solve an equation, the expression must be equated to a value, such as x²+2x+1=0
December 14, 2015

Physics
This is an elastic impact problem. Impact problems have one available equation, namely conservation of momentum. m1u1+m2u2=m1v1+m2v2. u, v represent initial and final velocities respectively, and m1, m2 are masses of bodies involved. Note that velocities have signs, e.g. ...
December 13, 2015

To Physics nerd
When expression exponents, please precede the exponent by the ^ sign. For example, 10² should be written as 10^2. 102 means one hundred and two, (write 10^2) 103 means one hundred and three, (write 10^3) Confusions will arise if the numbers are not expressed correctly.
December 13, 2015

French
Hint: un repas
December 13, 2015

Discrete Mathematics. Need Help
For R to be an equivalence relation, it must satisfy all the following conditions: 1) Reflexivity, i.e. (a,b)R(a,b) ∀(a,b). 2) Symmetry, i.e. (a,b)R(c,d) => (c,d)R(a,b) 3) Transistivity, i.e. (a,b)R(c,d) and (c,d)R(e,f) => (a,b)R(e,f). Use the definition of R to ...
December 13, 2015

Cht Ningi
T(9)=29.............9th term T(22)=55............22nd term If the AP is T(n)=T(n-1)+d, then d=(T(22)-T(9))/(22-9)=26/13=2 T(1)=T(9)-(9-1)d = 13 and therefore T(n)=11+2n T(1)=13 T(60)=11+120=131 To find the sum of the 1st to the 60th term, we use Little Gauss's method: T(1...
December 6, 2015

Physics
This we need to make two assumptions: 1. The car is on a perfectly horizontal plane/road 2. The car is in neutral AND friction is negligible. Use Newton's second law: F=ma F=400N m=(200 + 50n ) kg n=number of bags. a=1 m/s^2 (acceleration is measured in m/s^2) Set up ...
December 6, 2015

Ap physics
Use continuity equation, namely the volume of sand coming out per second equals the diameter * speed of sand. Volume = 75 L/min = 1.25 L/s Total area of jets (d=diam in dm) =2π(d²)/4 Speed of sand = 45 m/s = 450 dm/s Equate volumes of sand 450*2π(d²)/4=1.25 d=...
December 6, 2015

Math
Let the number be x. then x+1/x=29/10 Solve for x. The answers are rational fractions.
December 5, 2015

Math
First we have to decide how many slices we cut the pizza! It could be 8, but inspiring from the mushroom of 4/16 slices, I assume it is a large pizza cut into 16 slices. Then we add up the fractions to get toppings to cover 3/4+5/8+4/16=26/16 of the pizza. Evidently, if we ...
December 5, 2015

Mechanical engineering
With a point load in the middle, draw the bending moment diagram, which is a triangle with zero at both ends, and linearly increasing to the middle at R1*L/2. In fact, the standard formula for the maximum bending moment for a centrally placed point load is PL/4. Review your ...
November 26, 2015

Physics 101
Increase in length = Length (m) * ΔT (° C) * coefficient of expansion (°-1)
October 20, 2015

Physics
0 HP if there is no friction, pulling at a steady speed on a level road does not do work. If there is kinetic friction μk, then F=force = μk * mg v=velocity = 10 m/s Power = F.v j/s = F.v watts
October 15, 2015

Finite
In the long run, it would be equivalent to 120 plays with 120*0.60=72 as revenue and the following payouts: 97 green at 0.95 22 yellow at 0.40 1 red at 11.00 Subtract payouts from revenue and divide by 120 plays to get gain on individual play.
October 13, 2015

Math
48+34=48+2+32=50+32=82
October 12, 2015

Physics
This is a free fall situation. The horizontal velocity has no effect on the time to reach ground. Vertical distance, X=0+(1/2)at^2 =0+(1/2)(-9.81)*3^2 =44 m approximately.
October 12, 2015

Physics
The "jerk" depends on the difference between static friction (the stickiness) and kinetic friction. The former is always greater than (perhaps or equal to) the kinetic friction. You need to estimate the mass m of the drawer, the force F required to overcome the ...
October 2, 2015

physics
Resolve the initial velocities into the horizontal component, vx =v0 cos(θ) and the vertical component, vy= v0 sin(θ) where θ=-20 degrees (below horiz.) The horizontal component is subjected to only air resistance which in general is neglected, so travels at ...
October 2, 2015

basic chemistry(projectile)
Use sum of potential and kinetic energies = constant when air resistance is neglibible. Potential energy = mgh at a height h from datum kinetic energy = (1/2)mv^2 when moving at a speed of v.
October 2, 2015

Physics - Inverted pendulum
* d²y/dt²
October 2, 2015

Physics - Inverted pendulum
Interesting problem. The vertical motion exerts an acceleration of d²y/dy² on the mass. Intuition tells me the mass will move on each side on successive vertical strokes, hence frequency = ω/2. Next time ask him to drill his calculus and give the bambin a mug ...
October 2, 2015

physics
In the absence of air resistance we can split the movement of the bullet into the vertical and horizontal components. The former is a free-fall. Using the kinematics equation below, we can solve for the time it takes to free-fall through 2.4 cm: S=(v0)t+(1/2)at^2 with v0=...
September 30, 2015

Physics
We have a right triangle ABC, CA lies on the equator, where C is the destination (where plane intercepts the equator). B is the initial position of the plane, and is immediately south of A. So AB=150 km, ∠ABC=30°. We need length of BC. Using definition of cosine, AB/BC...
September 30, 2015

Physics
The faster automobile is basically playing a catch-up game, with a distance (gap) of 146 m. at a catch-up speed of 72.5-55.5=17 km/h. Converting this speed to m/s: 17 km/h = 17*1000 m/3600 s = 4.72 m/s How long will it take to catch up a distance of 146m at a speed of 4.72 m/s...
September 30, 2015

Physics
ignoring air resistance, we can apply the kinematics equation v1^2-v0^2=2aS S=distance travelled = 3 m v0=initial velocity (to be found) v1=final velocity =0 m/s at highest point a=acceleration due to gravity = -9.81 m/s^2 Solve for v0 and show that it is approximately 7.7 m/s...
September 29, 2015

Physics-Urgent
1. draw a free-body diagram. 2. Let T be the tension in each of the wires, which makes an angle of 27° with the vertical. 3. Sum forces on the sign in the y-direction (vertical) to get 2Tcos(27°)=23kg * 9.81 Solve for T.
September 27, 2015

Cryptography
I am not sure if I understand what you're supposed t find. But here's what I have found. I have mod(23*17,26)=1 (and not 9), so 23 cannot be the multiplier. I found it by trial and error, that mod(25*17,26)=9, (encrypting) mod(25*9,26)=17, (decrypting). So 25 is the ...
September 27, 2015

Stats
P(A and B) represents the probability that both events A and B occurring. Physically, it means that a person has both private and government insurance, which is unlikely. The probability of having any insurance is the sum of the two probabilities, i.e. P(A or B) = P(A) + P(B...
September 27, 2015

Phyics
If we assume uniform acceleration, we can use: ΔX=(v0)t+(1/2)at^2 v0=initial velocity = 0 m/s t=time=8.6 s ΔX=displacement=0.1994 m Solve for a (in m/s^2)
September 26, 2015

Physics
It is decelerating over the three seconds, with v0=initial velocity=+58 m/s acceleration due to gravity, a = -9.81 m/s^2 time, t=3 s Use kinematics equation: Displacement=(v0)t+(1/2)at^2 Substitute above values to get displacement.
September 26, 2015

physics
Use v1^2-v0^2 = 2aS v1=final velocity v0=initial velocity a=acceleration S=distance Use an appropriate frame of reference such as positive = upwards.
September 25, 2015

physics
Use v1^2-v0^2 = 2aS v1=final velocity v0=initial velocity a=acceleration S=distance Use an appropriate frame of reference such as positive = upwards.
September 25, 2015

Z table
Draw a sketch of what you want, similar to this: http://prntscr.com/8kitsp THen look up the standard normal distribution table (left tail) the number of standard deviations that correspond to 92%. (it should be between 1.4 and 1.5). Since each standard deviation corresponds to...
September 25, 2015

physics
This is an expression derived from Bernoulli's equation, so use all the values and substitute in the given equation, making sure that the dimensions are compatible. Check dimensions (C is dimensionless) F=(1/2)CAρv^2 =m^2*kg/m^3*(m/s)^2 =m-kg/s^2 = same unit as Newton...
September 25, 2015

Physics
Please start with a free-body diagram, then resolve forces parallel and normal to the slope. See http://prntscr.com/8kinmn Assuming the skier (the round object) is moving up the slope, then the friction force is towards downslope. The towbar force is therefore, equating forces...
September 25, 2015

physics
Like this? http://prntscr.com/8kiqq7 But we need the height of the building, H.
September 25, 2015

physics
Use v1^2-v0^2=2aS v1=final velocity v0=initial velocity (0 for a free-fall) a=acceleration due to gravity (=-9.81 m/s^2) S=-38.5m solve for v1.
September 25, 2015

physics
v0=15.5 v1=0 v1=v0+at Solve for t=(0-15.5)/(-9.81)=1.580 sec. So it will return to the same elevation as it left off in 2*1.580=3.16 s. Instead, it took 3.3-3.16=0.14 sec. more Using the free-fall equation for H, H=(1/2)gt^2, we have H1=(1/2)g(1.580)^2 H2=(1/2)g(1.720)^2 ...
September 24, 2015

Physics
Use v1^2-v0^2=2(a)(Δx) or Δx = (v1^2-v0^2)/(2a) a=acceleration, v0=initial velocity v1=final velocity Do not forget to convert km/h to m/s to get your answer in metres.
September 24, 2015

Physics
First find from the book or Internet the Young's modulus (E) for aluminium. I use E=69 GPa for aluminium. Using stress = force (mg) / cross sectional area ε=Strain = extension/unit length = stress/E stretching = extension =ε * length =stress*length/E you ...
September 24, 2015

physics
Average velocity = (change in position)/time Assume initial position = (0,0) First determine the displacement of the train at the end of the trip: movements(N): 1. 43 km/h for 20 min = 43/3 km due east 2. 43 km/h for 25 min at N54E = 43*25/60 km at CCW 36° from due east 3...
September 24, 2015

physics
It is a question which requires an unreasonable assumption, namely ignore air-resistance. Without air-resistance, time it takes to reach ground is t=sqrt(2H/g) =sqrt(2*10000/32.2) =24.9 s The horizontal velocity of the plane does not change the time required. If the dimensions...
September 24, 2015

Physics
a) correct. b) use t=sqrt(2h/g) Time to go up: h=5.1m Time fall back to the ground: h=7.1m Add the two times to get your answer.
September 23, 2015

probabilty
Have you done Baye's theorem, total probability and conditional probability? If not, you need to review these topics before you can tackle this problem. Here the assumption is not clear, but I will assume that it is equally probable to 1. pick one of the 4 baskets 2. pick ...
September 23, 2015

Physics
Time to free-fall 35.56m = sqrt(2*S/g) = sqrt(2*35.56/9.81) = 2.6925 s Horizontal velocity does not change during free fall, so v= Dist/time = 10.36 m/2.6925s = 3.81 m/s
September 23, 2015

Physics
Horizontal velocity does not change in a free-fall, so time = distance/velocity = 146.8/29.33 = 5.0051 s. (keeping 5th significant fig.) Initial vertical velocity = 0 for free fall, so H=(1/2)at^2 =(1/2)*(-9.81)(5.0051^2) =-122.9 m Ans. the ground is 122.9m below the cliff.
September 23, 2015

Physics
Assuming zero friction, the additional force is the equilibrant. We have a force of +480 N and -920 N. The equilibrant is the negative of the vector sum, namely -(480-920)=440 N, i.e. 440 N in the same direction as the 480N force. If friction is present, some additional steps ...
September 5, 2015

finite math
*correction I get a little less than 2500.
September 4, 2015

finite math
If you make N=27 annual payments of A=$175 with annual interest of i=0.053, the future value is FV=A(1+R+R^2+...+RN-1) =A(RN-1)/(R-1) =A(RN-1)/i where R=1+i The present value is then PV=FV/(RN) =A(RN-1)/(i*RN) I get a little over 10000.
September 4, 2015

Math
Use equality of proportions object:shadow x:12 = 5 m : 6 m which means x/12=5/6 Cross multiply: 6x=5*12 Solve for x x=60/6=10 So the tree is 10 m tall
August 26, 2015

BUSINESS CONSULTING
Hmm...It would be nice if you start working on the problem, show some thoughts and work of your own, identify the difficulties, so that we can help you.
August 25, 2015

Math
Hint and example: distributive property means the equivalence of the following expressions: a(b+c) = ab + ac Example: 5(x+4) = 5x + 5(4) = 5x + 20
August 25, 2015

Math
A typical line in slope intercept form is y = mx + b where m is the slope and a is the y-intercept. Two lines are parallel whenever their slopes (m1, m2) are identical. Try to spot two lines with identical slopes and find the corresponding choice of answer.
August 10, 2015

math
Solve for x from the equation: 5x-4 = 2(2x+10) 5x-4 = 4x + 20 5x-4x = 20+4 x=24 so angle ABC = 5(24)-4 = 120-4=116 degrees. What kind of angle is angle ABC?
August 10, 2015

French SraJMcGin
To Rose: If you mean : "if you make up the sentences in English and translate it to French, how to make sure it will be translated to the subjunctive" then SraJMcGin has already given you all the conditions that the sentence should be subjunctive in French. The ...
July 17, 2015

math
Please refrain from starting a new thread when information refers to a previous thread.
June 15, 2015

math
"last one is $300" So you would write a table as follows Date description amount Balance -......bal.brought fwd - 2000 Jan 2...deposit 500 2500 Jan 10..Alex co. 600 1900 Jan. 16 Angels co. 300 --?-- So you can calculate the final balance on the last line.
June 15, 2015

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