Thursday
December 8, 2016

Posts by Reiny

Total # Posts: 36,913

Maths Unitary Method
The key word in the first part is "or" men's rate = 875/5 = .. women's rate = 875/7 = ... then 10(men's rate) + 7(women's rate) = ... (politically incorrect question)
August 19, 2016

Maths Percentage
what is 54000/1.1 ?
August 19, 2016

Maths Compound Interest
count = 512000(1.025)^2 = .....
August 19, 2016

Maths Compound Interest
When is 1000(1.10)^n = 1331 ? 1.1^n = 1.331 take log of both sides, and use log rules n log 1.1 = log 1.331 n = log 1.331/log 1.1 = .... you do the button pushing
August 19, 2016

geometry
Well, you know that that the area of a triangle = (1/2)bh, where b is the base and h is the height but you are told that h = 3b , so area = (1/2)(b)(3b) 27 = (1/2)(3b^2) times 2 54 = 3b^2 b^2 = 18 b = √18 or 3√2 ft base = 3√2 ft and the height is 9√2 ft...
August 19, 2016

Correction - Maths
I obviously got x = 360 So there are 360 marbles, I have no idea where I got the 510 from, and then I copied it again at the end. Time for my third cup of coffee.
August 19, 2016

Maths
let the total be x (2/5)x = r , also b+54 = (2/5)x b = 2x/5 - 54 = (2x - 270)/5 b : y = 5 : 7 5y = 7b y = (7/5)b y = 7(2x-270)/25 so 2x/5 + (2x-270)/5 + 7(2x-270)/25 = x times 25 10x + 10x - 1350 + 14x - 1890 = 25x -9x = -3240 x = 360 we have 510 marbles check: red = (2/5)(360...
August 19, 2016

math
I had done this for you. http://www.jiskha.com/display.cgi?id=1471418592
August 17, 2016

Analytic Geometry
Since you know the vertex, your equation must be x = a(y-0)^2 + 0 , if the axis of symmetry is horizontal x = ay^2 but (3,5) lies on it, so 3 = a(25) a = 3/25 x = (3/25)y^2 or 25x = 3y^2
August 17, 2016

Maths
cos(A+B) = cosAcosB - sinAsinB apply it to your question
August 17, 2016

Math
log3 9^4 = 4 log3 9 = 4(2) = 8 or , just think it through 9^4 = 3^8 so log3 3^8 must be 8
August 17, 2016

math
first number --- x 2nd number ---- 1/x x + 1/x = 3 x^2 + 1 = 3x x^2 - 3x + 1 = 0 using competing the square: x^2 - 3x + 9/4 = -1 + 9/4 (x + 3/2)^2 = 5/4 x + 3/2 = ± √5/2 x = -3/2 ± √5/2 x = (-3 + √5)/2 or x = (-3 - √5)/2
August 17, 2016

Math
assuming that "a" is the base - log a x^6 y^7 = -(loga x^6 + loga y^7) = -(6loga x + 7loga y) = -6loga x - 7loga y none of your choices are correct, unless there is a typo with that minus sign
August 17, 2016

Math3c
Just use the definitions of an AP and translate the English to Math. "the sum of the first three terms" = a + a+d + a+2d = 3a + 3d "the sum of the next four terms" = a+3d + a+4d + a+5d = 3a + 12d given: "the sum of the first three terms is one half the...
August 17, 2016

Pre Cal
Show me your expansion, and I will check it. Did you remember that i^2 = -1 ?
August 17, 2016

Pre Cal
take a look at this question I did several years ago http://www.jiskha.com/display.cgi?id=1315862859
August 17, 2016

Calculus
I will assume you mean: y = x^3 + 3x^2 , notice how we show exponents here x^3 + 3x^2 = 0 x^2(x + 3) = 0 finish it up
August 17, 2016

math
wherever you see y, replace it with 2 and evaluate
August 17, 2016

Algebra
1. let his actual speed by x km/hr time to do his 40 km trip = 40/x let his supposed speed be x+1 km/h time taken = 40/(x+1) 40/x - 40(x+1) = 2 times x(x+1) , the LCD 40(x+1) - 40x = 2x^2 + 2x 2x^2 + 2x - 40 = 0 x^2 + x - 20 = 0 (x+5)(x-4) = 0 x = 4 or a negative he went at 4 ...
August 17, 2016

Math
clearly, (f + g)(x) = 5x - 3 which is linear, thus the domain is the set of all real numbers.
August 17, 2016

Math
For P(a,b) and Q(c,d) the midpoint M is ( (a+c)/2 , (b+d)/2 ) apply this to your problem
August 17, 2016

math
cost price of cheaper chocolates = 1.50/10 = .15 each cost of expensive chocolates = .20 let the number of each type of chocolates be x cost price = .15x + .2x = .35x selling price = 4/20 = .2 each return on sale = 2x(.2) = .4x .4x - .35x = 10 .05x = 10 x = 200 he bought 200 ...
August 17, 2016

math
Hard to understand your notation. I will assume you mean: 4.5 kg at 600 per kg ----> 2700 2 kg at 1200 per kg -----> 2400 3 kg at 1500 per kg -----> 4500 total = 9600 leaving 10000-9600 = 400
August 17, 2016

math
did you mean "Roman numeral" ? 1959 ----> MCMLIX http://www.rapidtables.com/convert/number/roman-numerals-converter.htm
August 17, 2016

physics question
Look at this question answered by Damon over 5 years ago, just change the numbers to fit your question. http://www.jiskha.com/display.cgi?id=1296412513
August 17, 2016

Pre-calc
6csc Ø - 5 = 1 csc Ø = 6/6 = 1 then sin Ø = 1 consider the sine curve and it is clear that Ø = π/2 or ±2π + π/2 or ±4π + π/2 ... for the given interval, Ø = π/2 general solution: Ø = π/2...
August 16, 2016

Math
The first question can be answered in 2 ways for each of those, the 2nd question can be answered in 2 ways, so 2^2 or 4 so far ... number of ways = 2^5 = 32
August 16, 2016

Calculus
by simple inspection, and knowing the rules of derivatives for sine and cosine .... no need for substitution. ∫sin(x)cos^2(x)dx = (-1/3) cos^3 x + c
August 16, 2016

math algebra
I assume you meant: 10, 2, 2/5, 2/25 clearly a = 10 , r = 1/5 you should know your formulas. term(n) = ar^(n-1) term(7) = 10(1/5)^6 = 10/15625 = 2/3125
August 16, 2016

algebra
Just did this. Why are you changing names and repeating the question ?
August 16, 2016

math
let the unit digit be x and the tens digit by y then the original number is 10y + x and the number reversed is 10x + y 10x + y - (10y + x) = 18 9x - 9y = 18 x - y = 2 but we also know that xy = 24 it should be obvious that the two number are 6 and 4. Since reversing the ...
August 16, 2016

Math
According to the wording of the question, your answer is correct Now -- 5 at end of month 1 = 5(2) = 10 at end of month 2 = 5(2^2) = 5(4) = 20 at end of month 3 = 5(2^3) = 5(8) = 40 ... at end of month 8 = 5(2^8) = 5(256) = 1280
August 16, 2016

Math
recall that area of triangle = (1/2) base x height 36 = (1/2)(base)(9) multiply both sides by 2 72 = 9base base = 72/9 = 8
August 16, 2016

Algebra
how about this way: using (ab)^n = (a^n)(b^n) (4x^-1)^-1 = (4^-1)(x^-1)^-1 = (1/4)(x^1) = (1/4)x or = x/4 #2 (x^3+3x^2+3x+1)^(-2/3) = 1/(x^3+3x^2+3x+1)^(2/3) notice I assumed your exponent was -2/3, the way you typed it, the exponent would have been -2 , with 3 a divisor ( (x^...
August 16, 2016

mathematical method
First of all let's expand this (2-i)(1+3i)(3+4i) = (2-i)(3 + 13i + 12i^2) = (2-i)(13i - 9) , remember that i^2 = -1 = 26i - 18 - 13i^2 + 9i = -5 + 35i magnitude = √(25 + 1225) = √1250 = 25√2
August 16, 2016

math
Their share of the profit should be proportional to the amount of their investment Total investment = 13000 Alex's share is 8000/13000 = 8/13 Ali's share is 5/13 So 5/8 = 2000/x , assuming Ali and Ally are the same person 5x = 16000 x = 3200 check: 2000 : 3200 = 5 : 8
August 16, 2016

Math
The distance between them is decreasing at a rate of 50 mph, (17+13) So in the last minute the distance to be covered is (1/60)(50) miles ----> recall, distance = rate x time = 5/6 of a mile
August 15, 2016

math
Don't become obsessed with formulas, just think it through. you want the distance around 1/2 of a circle = (1/2)(2π(30)) = 30π Then you must add the diameter, which would be 60 cm total = 30π + 60 which looks like πr + 2r
August 15, 2016

Help on PreCalc
As usual, make a sketch of a right-angled triangle and using Pythagoras, r^2 = 8^2 + 15^2 = 289 r = 17 π<α<3π/2 ----> α is in quadrant III sin α = -15/17 and cos α = -8/17 recall cos 2A = 1 - 2sin^2 A thus: cos α = 1 - 2sin^2 (α...
August 15, 2016

Maths
"1/3 of boys and 1/4 of girls." is not a complete sentence. What about the 1/3 of boys and 1/4 of girls ?
August 15, 2016

Pre-calc
tan2θ=7/11 ​; π<2θ<3π/2 so 2Ø is in quadrant III and Ø is in quadrant II construct a right-angled triangle, with angle 2Ø, opposite side as 7, and adjacent side as 11 the hypotenuse is √170. Remember 2Ø is in ...
August 13, 2016

Pre-calc
As Steve and Damon pointed out to you earlier, sin(α−β) = sinαcosβ - cosαsinβ given: tanα=5/7 and sinα<0 , so by the CAST rule α must be in quadrant III since tanα = 5/7, by Pythagoras, the hypotenuse of our triangle ...
August 13, 2016

Algebra
So go ahead and simplify the expression that Steve gave you.
August 12, 2016

math
let the size of the cut-out be a square of side x inches base = (8-2x) by (11.75 - 2x) and the height is x x(8-2x)(11.75-2x) = 63.75 x(94 - 39.5x + 4x^2) = 63.75 94x - 39.5x^2 + 4x^3 - 63.75 = 0 don't know what method you know to solve a cubic, I ran it through Wolfram and...
August 11, 2016

Calc
let the angle between the two equal sides be Ø area = (1/2)(L)(L)sinØ , (you should know that formula) d(area)/dØ = (1/2)L^2 (-cosØ) , where L is a constant for a max of area (1/2)L^2(-cosØ) = 0 cosØ = 0 but of course cos 90° =0 ...
August 11, 2016

Algebra
Assuming that each way is 400 miles, (even though in Rome they wouldn't know what miles are, and would be using km.) let speed of plane in still air be x mph let speed of wind be y mph going with the wind: 5(x+y) = 400 ---> x + y = 80 going against the wind: 10(x-y) = ...
August 11, 2016

precal
x2 - 6x + 5y = -34 5y = -x^2 + 6x - 34 = -1(x^2 - 6x + 9 - 9) -34 = -(x-3)^2 + 9 - 34 y = (-1/5)(x - 3)^2 - 25/5 y = (-1/5)(x-3)^2 - 5 lots of algebraic typing ahead, so I will let you watch 4 great videos dealing with this topic by the remarkable Mr. Khan https://www....
August 11, 2016

Maths
roots of 4x^2-16x+15=0 are a and b, (for alpha and beta) by the properties of roots of a quadratic a+b = -(-16/4) = 4 ab = 15/4 new roots: a/b and b/a sum of new roots = a/b + b/a = (a^2 + b^2)/(ab) now a^2 + b^2 = (a+b)^2 - 2ab = 4^2 - 2(15/4) = 17/2 so sum of new roots = (17...
August 11, 2016

Math
My money is on Henry's solution
August 11, 2016

Pre-calc
That's not what you had originally. Glad you changed it, now my solution should make sense to you.
August 11, 2016

Pre-calc
The wording of your question makes no sense to me. Do you want csc(5π/6) as found on the unit circle? We have an ordered pair associated with (5π/6) , not csc(5π/6) I strongly suggest you print out one of the many unit circle diagrams available. Here is one of ...
August 11, 2016

correction - Math
easier way (and correct answer) : let the cost of a tie be $x cost of a shirt = $(x+50) 4x + 7(x+50) = 746 4x + 7x + 350 = 746 11x = 396 x = 36 Each tie costs $36, (and a shirt costs $86) expensive tastes!
August 11, 2016

Math
8 men mow 4 identical greens in 20 minutes 2 men mow 1 identical green in 20 minutes 6 men mow 1 identical green in 60 minutes
August 11, 2016

Math
2400 hectares of canola in 12 days using 4 machines 600 hectares of canola in 12 days using 1 machine 3600 hectares of canola in 12 days using 6 machines or time is directly proportional with the acreage and inversely with the number of machines T = k (A/M) given: 12 = k(2400/...
August 11, 2016

Maths
I don't see a quadrilateral bounded by only 3 sides.
August 10, 2016

algebra
Just translate the English to Math: let the height be x ft "the width is 3 times longer than the height" ---> width = 3x "the length is 9 times longer than the height" -----> length = 9x Now use the given to form your equation x(3x)(9x) = 64 27x^3 = ...
August 10, 2016

algebra
fix typo
August 10, 2016

Math
52728 = 3 x 2^3 x 13^3, and (2^3 x 13^3) is a perfect cube so dividing 52728 by 3 would leave a quotient of 17576 which is 2^3 x 13^3 or 26^3 thus the smallest such number as a divisor is 3 and the cube root of the quotient is 26
August 10, 2016

maths
In a parallelogram, adjacent angles must add up to 180° 4x-15 + 5x-3 = 180 I will let you finish it.
August 10, 2016

Math
sin Ø = 3/5 , so Ø could be in quadrants I or II make a sketch of the triangle and you should recognize the 3-4-5 right-angled triangle. the cosØ = 4/5 if Ø is in I and cosØ = - 4/5 if Ø is in II
August 10, 2016

Math
original fraction ---- x/(x+1) new fraction = (x-2)/(x-1) (x-1)/(x-2) + 4x/(x+1) = 5 times (x-2)(x+1), the LCD (x-1)(x+1) + 4x(x-2) = 5(x-2)(x+1) x^2 - 1 + 4x^2 - 8x = 5x^2 - 5x - 10 3x - 9 = 0 x = 3 original fraction is 3/4 check: new fraction = 1/2 1/(1/2) + 4(3/4) = 2 + 3...
August 10, 2016

math
total of pages ---- x 120 + .15x + .1x + 60 = x solve for x
August 9, 2016

probability
what is 360/(360+318) ?
August 9, 2016

probability
what is (61/100)(640) rounded to the nearest whole number ?
August 9, 2016

probability
use the concept that Bob showed you here: http://www.jiskha.com/display.cgi?id=1470754142
August 9, 2016

Opt math URGENT
RS = (1/16)(-6cosØ) I picked a random angle, Ø = 25 LS ≠ RS the equation is not true, thus we can't prove the identity
August 9, 2016

Maths
routine right-angled triangle trig x/3.8 = cos 65 x = 3.8cos 65° take over
August 9, 2016

Math
4x + 3.0 = -4x + 2.6 4x + 4x = 2.6 - 3.0 carry on, it is easy
August 9, 2016

Math
Start with the unit x x 1 x 6 1 -2 6 1, no way x 7 2 -1 7 2 , no way x 8 3 0 8 3 , not really a 3 digit number >b>1 9 4 ---- looks good 1 10 5 , no way
August 9, 2016

Math
"of" usually means multiplication , not subtraction, so you want (1/8)(12) = 12/8 = 3/2
August 9, 2016

math
smaller number --- x next consecutive number ---- x+1 3(1/(x+1)) - 1/x = 3/10 multiply each term by 10x(x+1), the LCM 30x - 10(x+1) = 3x(x+1) 30x - 10x - 10 = 3x^2 + 3x 3x^2 - 17x + 10 = 0 (x - 5)(3x - 2) = 0 x = 5 or x = 2/3 but our number was to be an integer, so x = 5 the ...
August 9, 2016

Maths
one number ---- x , the larger the other --- 14-x x(14-x) = 40 14x - x^2 = 40 x^2 - 14x + 40 = 0 (x-10)(x-4) = 0 x = 10 or x = 4 the two numbers are 10 and 4.
August 7, 2016

Maths
No typo, the solution is correct first case was 2 years ago 2nd case is 6 years from now what is the time difference? Husnain, I even checked to show you that answer is correct.
August 6, 2016

Maths
2 years ago: Susie---- x Ronald --3x 6 years from now: Susie = x+8 Ronald = 3x + 8 3x+8 = 2(x+8) x = 8 2 years ago, Ronald was 24 So now he is 26 check: ages now: Ronals --- 26 Susie ---- 10 6 years from now Ronald will be 32 Susie will be 16 Ronald is twice as old as Susie, ...
August 6, 2016

ratio and proportions
number of rabbits ---- x number of cats ------- 2x number of dogs ----- 3(2x) = 6x 6x - 10 = x 5x = 10 x = 2 so 2 rabbits 4 cats 12 dogs
August 6, 2016

Math
S(1) = 1/(1*2*3) = 1/6 S(2) = 1/6 + 1/(2*3*4) = 1/6 + 1/24 = 5/24 S(3) = 5/24 + 1/(3*4*5) = 5/24 + 1/60 = 9/40 Wolfram said: http://www.wolframalpha.com/input/?i=1%2F(1*2*3)+%2B+1%2F(2*3*4)+%2B+1%2F(3*4*5)+%2B+...+%2B+1%2F(n*(n%2B1)*(n%2B2))
August 6, 2016

math
−4≤2x+6<18 subtract 6 -10 ≤ 2x < 12 divide by 2 -5 ≤ x < 6 remember, only multiplication and division by a negative number will affect the inequality sign. Since I multiplied by +2, nothing happened.
August 6, 2016

algebra
let's assume you have 1/√(x+1) multiply top and bottom by √(x+1) 1/√(x+1) * √(x+1)/√(x+1) = √(x+1)/(x+1)
August 6, 2016

math
correct
August 6, 2016

Algebra
If you meant: (1/2)x(2x-4)^2 = (1/2)(x)( 2(x-2) )^2 = (1/2)(x)(2^2)(x-2)^2 = (1/2)(x)(4)(x-2)^2 = 2x(x-2)^2 ----> that answer was correct or 2x^3 - 8x^2 + 8
August 5, 2016

Algebra
smaller number ---- x "The larger of two numbers is 5 less than twice the smaller number" ---> 2x - 5 Now just translate: "The sum " ---> + "The sum of [four times the larger] and [twice the smaller number] ---> 4(2x-5) + 2x " is 100"...
August 5, 2016

Incorrect Subject label - Maths
discussed here: http://www.jiskha.com/display.cgi?id=1412345782
August 5, 2016

ALGEBRA
this has been answered
August 5, 2016

A
Once you see the pattern, listing 7 numbers in each case is a trivial problem. Option 1 - they tell you the pattern Option 2 - square the numbers Option 3 - double the previous number
August 5, 2016

Math
6 workers do 1 km in 4 days 1 worker does 1 k m in 4/6 or 2/3 days 4 workers do 1 km in 8/3 days 4 workers do 3 km in 3(8/3) or 8 days
August 4, 2016

insight academy
amount invested at 10% -- x amount invested at 12% ---- 12000 - x .10x + .12(12000 - x) = 1280 easy to solve for x
August 4, 2016

Math
you probably meant: A= (x+4)/(xsquared+9x+20) = (x+4)/((x+4)(x+5)) = 1/(x+5) , x ≠ -4 B = (3xsquared-9x)/(xsquared+3x-18) = 3x(x - 3)/((x+6)(x-3)) = 3x/(x+6) , x ≠ 3 clearly they are not equivalent I am sure you can handle the algebra from this point.
August 3, 2016

math
value = mt + 1500 when t = 4, value = 800 800 = 4m + 1500 4m = -700 m = -175 value = -175t + 1500 plug in t = 5 to find value
August 3, 2016

someone please help me. - Precalc
y=cos(x−5π/2) amplitude = 1 period = 2π If we had the simple curve y = cos x the quarter points would be (0,1) , (π/2, 0) , (π, -1), (3π/2 , 0) , and repeating at (2π, 1) but we shifted our basic cosine curve 5π/2 units to the right, so...
August 3, 2016

Math
It says f'(x) = 2x-1 for x ≤ 1, so x = 1 is included and valid for f'(x) to get f'(1) = 1 for x ≤ 1, f(x) = x^2 - x + c which is a parabola opening upwards, we don't know c but notice that when x = 1 , f(1) = c so it "ends" at (1,c) for x&...
August 3, 2016

Math
height --- 4.9 base --- 3.9 area = (1/2)base x height = ...
August 3, 2016

Math Problem
lots of "dogs and chicken" problems listed below in Related Questions. Take a look at some of them
August 3, 2016

Math
Think about where the zeros can come from 1! = 1 , 2! = 2 , 3! = 6 , 4! = 24, 5! = 120 <-- our first zero ..... 10! = 3628800 <-- our 2nd zero that is, a zero comes from a number ending in 2 multiplied by a number ending in 5, or by a number ending in 0 so the zeros ...
August 3, 2016

maths
cost price ---- x final selling price = 1.04x but that represents 90% of the marked price so the marked price = 1.04x/.9 = 1.1555...x so the marked price is 15.55..% higher than the cost price. e.g. suppose the cost price is $100 marked up price = 100(1.155...) = 115.56 now ...
August 3, 2016

math
suppose you had 5 bags and each bag would contain 6 apples. How many apples would you have? What operation did you just perform? Do the same for your question.
August 3, 2016

calculus
height = -4.9t^2 + vt+ c but it said "groundlevel" ---> c=0 height = -4.9t^2 + vt 0 = -4.9(400) + 20v 20v = 1960 v = 98 So the initial velocity was 98 m/s height = -4.9t^2 + 98t d(height)/dt = -9.8t + 98 = 0 at maximum height -9.8t + 98 = 0 t = 10 seconds (We ...
August 2, 2016

Math
routine right-triangle trig. cos35° = 42/hypotenuse hypotenuse = 42cos35 = 34.4 ft to the nearest whole number, 34 ft
August 2, 2016

math
It gets even more complicated when you consider that more than likely compound interest would have been used. So at what rate are 24 payments equivalent to a present value of 3438 ? 165(1 - (1+x)^-24)/x = 3438, where x is the monthly rate tough to solve, used Wolfram: http://...
August 2, 2016

maths
number of boys ---- b number of girls ----- g b = 4g + 3 b-3 = 4g g= (b-3)/4 e.g. let the number of boys be 43 then girls = (43-3)/4 = 10 4 times the number of girls plus 3 = 4(10)+3 = 43 which is the number of boys
August 2, 2016

Math
They would be separating at 500 ft/min time to go 3000 ft at that speed = 3000/500 min or = 6 minutes or time taken --- x minutes distance of one student = 300x distance of other student = 200x 300x + 200x = 3000 500x = 3000 x = 6 , just like above.
August 2, 2016

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