Thursday
September 29, 2016

Posts by Reiny

Total # Posts: 36,058

Math
40 : 60 : 120 : 140 = 4 : 6 : 12 : 14 = 2 : 3 : 6 : 7
August 26, 2016

value
from what you have: Logx + logy=4 logx +2logy=3 log(xy) = log(x^4 y^2) = 3 so : log(xy) = log(x^4 y^2) x^4 y^2 = xy x^3 y = 1 y = 1/x^3 , of course x > 0 in logx + logy = 3 logx + log(1/x^3) = 3 log(x(1/x^3)) = 3 log (1/x^2) = 3 1/x^2 = 10^3 = 1000 1000x^2 = 1 x^2 = 1/1000 ...
August 26, 2016

maths reiny help!!
I just copied my previous solution and changed the numbers: Suppose that the cost of each of the original books was $x per book So the cost was 80x He got a 15% discount, so the cost was (.85)80x = 68x but for 68x he actually got 90 books so the cost of each book was only 68x/...
August 26, 2016

algebra
width ---- w length ---- w+6 width*length = area w(w+6) = 72 w^2 + 6w - 72 = 0 (w-6)(w+12) = 0 w = 6 or w = a negative the width is 6 cm with only a few nice choices you could have easily checked each one in your head e.g. for the first one: is 10 times 16 equal to 72 ? NO etc
August 26, 2016

Math
cows --- x chickesn --- y x+y = 12 ** 4x + 2y = 28 or 2x + y = 14 *** subtract ** from *** x = 2 then y = 10 2 cows and 10 chicks
August 26, 2016

math
2 workers takes 15 hours to make 3 fireplaces 2 workers takes 5 hours to make 1 fireplace 2 workers takes 20 hours to make 4 fireplaces 1 worker takes 40 hours to make 4 fireplaces 5 workers takes 8 hours to make 4 fireplaces or it takes 30 work-hours to make 3 fireplaces it ...
August 26, 2016

Maths
let Katie's present age be k let Melanie's present age be m Five years ago: Katie ---- k - 5 Melanie -- m-5 k-5 = 10(m-5) k - 10m = -45 ** 2nd condition: Katie's age in 15 years = 3(Melanies age in 11 years) k + 15 = 3(m + 11) k+15 = 3m + 33 k - 3m = 18 *** ...
August 25, 2016

MAth
I did this for you yesterday http://www.jiskha.com/display.cgi?id=1472041460 Why are you repeating it? btw, it should say "How many complete revolutions are needed?"
August 25, 2016

Math help
recall that cot^2 x +1 = csc^2 x so ∫(cot⁡^2 x-csc^2 x)^2dx = ∫(cot⁡^2 x-(cot^2 + 1)^2dx = ∫ -1 dx take over
August 25, 2016

MATHS
what is 1 - .8(.7) ?
August 25, 2016

Math
add 246 to both sides
August 24, 2016

Math
correct
August 24, 2016

Math
Since a constant multiplier is not usually written behind a binomial, I suspect you meant: (x+1)^2 = 9 then x+1 = ±√9 = ±3 x+1 = 3 ----> x = 2 or x+1 = -3 ---> x = -4
August 24, 2016

MAV school
x/4 + (120-x)/5 = 28 times 20 , the LCD 5x + 4(120-x) = 560 5x + 480 - 4x = 560 x = 80 so we split them up as 80 and 40 , with the 80 being divided by 4 and the 40 divided by 5 check: 80/4 + 40/5 = 20+8 = 28
August 24, 2016

MAth
Circumference of barrel = 56π cm number of rotations = 2944/(56π) = appr 16.7
August 24, 2016

MATHS PLZZ HELP PLZZ SOMEONE KINDA BEG YOU
Suppose that the cost of each of the origininal bools was $x per book So the cost was 50x He got a 10% discount, so the cost was (.9)50x = 45x but for 45x he actually got 60 books so the cost of each book was only 45x/60 = 3x/4 As a percentage: (3x/4) / x = 3/4 or 75% which ...
August 24, 2016

math
The assumption would be that he would be randomly guessing at the answer. Since 12/15 = .8, why did you not include the probability of getting 12 correct out of the 15 ? Try adding that to your other cases. For b) wouldn't getting 20 out of 25 correct yield 80% ? Same for ...
August 24, 2016

Math
clearly I have a typo in the 3rd last line, should be = 2^2011 (-√3/2 + (1/2) i )
August 24, 2016

Math
let's use De Moivre's Theorem let z = √3 - 1 sketching it in the Argand plane will give you |r| = 2, and tanØ = -1/√3 Ø = 330° or 11π/6 z = 2(cos 330° - i sin 330°) z^2011 = 2^2011(cos (663630°) - i sin(663630°) ) ...
August 24, 2016

Math
By "a complete sketch" they very likely want a right-angled triangle. since tanØ = opposite/adjacent = 3/4 and the angle is in the third quadrant y = -3 and x = -4 r^2 = 9 + 16 = 25 r = 5 sin Ø = -4/5 cos(Ø + 180) = cosØcos180 - sinØ...
August 23, 2016

Maths
circumference of wheel = πd = .98π metres number of rotations = 1540 m/.98π m = 531.898.. = appr 532 rotations how did you get 500?
August 23, 2016

Maths
I will assume that you meant: (cosecθ-cotθ)^2=(1-cosθ)÷(1+cosθ) or else the identity is not true. LS = (1/sinØ - cosØ/sinØ)2 = (1-cosØ)^2 / sin^2 Ø = (1 - cosØ)(1-cosØ)/( (1 - cosØ)(1 + cos&...
August 23, 2016

math
What is 1.74 / 0.29 ?
August 23, 2016

Math
width or breadth ----- x cm length --------------- 3x - 2 solve for x, and sub back into my definitions 2x + 2(3x-2) = 60
August 23, 2016

statistics
number of "not reds" is 20 so prob(not red) 20/26 = 10/13 or prob(red) = 6/26 = 3/13 prob(not red) = 1 - 3/13 = 10/13
August 23, 2016

math
(3^-3)x = 4 (1/3^3)x = 4 (1/27)x = 4 x = 108
August 23, 2016

Correction - Maxwell
How did you get your answer? It is not correct Felicia's present age .... f Tom's present age ........ t 3f = t+4 ** f+3 + t+3 = 30 f+t = 24 t = 24 - f *** sub *** into ** 3f = 24-f + 4 4f = 28 f = 7 then t = 24-7 =17 Felicia is now 7 and Tom is now 17 check: three ...
August 23, 2016

Math
If exterior angle is 50°, then each interior angle is 130° let the number of sides be n , where n is a whole number sum of interior angles = 180(n-2) each interior angle is 180(n-2)/n 180(n-2)/n = 130 180n - 360 = 130n 50n = 360 n = 7.2 , silly answer, so nope, not ...
August 22, 2016

Math
slope of a line is the tangent of the angle that the line makes with the horizontal, so slope = rise/run = 225/1000 = 9/40 so the hypotenuse of the corresponding triangle is √(40^2 + 9^2) = √1681 cosine (angle) = 40/√1681 = 40/41
August 22, 2016

Math
unit digit of original number ---- x tens digit of original number ---- x+5 original number = 10(x+5) + x = 11x + 50 number reversed = 10x + (x+5) = 11x + 5 11x+50 + 11x + 5 = 99 22x = 44 x = 2 the original number was 72 check: 72 + 27 = 99 , my answer is correct
August 22, 2016

Math
well, |-9| = 9 so you have -9/9 = -1
August 21, 2016

Math
you got it 7 - √11
August 21, 2016

Algebra
I assume you meant: |t-2| = -1 since by definition |anything| is never negative, there is no solution.
August 21, 2016

math
Ok, who is stopping you ?
August 21, 2016

math
each of the other equal sides ---- x cm x^2 + x^2 = 98^2 2x^2 = 9604 x^2 = 4802 x = √4802 = 49√2 cm
August 21, 2016

theory of probability
What you have is the total number of ways to place the caps Let's actually list them, there are only 6 I will write them as a pair of digits, where the first number is the bottle and the second digit is the cap 11 22 33 ----> all correct 11 23 32 ----> 1 right, 2 ...
August 21, 2016

Maths Percentage
(1.25x)(r) = x 1.25r = 1 r = 1/1.25 = .8 = 80% So it must be reduced by 20% check: suppose the original was $100 after the increase it would be 125 after a reduction of 20% is would be .8(125) = 100
August 21, 2016

Math
2000(1+i)^2 = 24200 (1+i)^2 = 1.21 take √ of both sides, etc
August 21, 2016

please help with this trigonometric identity!
I am sure that you meant: (cos 'a' - cos 'b') / (sin 'a' + sin 'b') + (sin 'a' - sin 'b') / (cos 'a' + cos 'b') = 0 the LCD is (sina + sinb)(cosa + cosb) LS = ( (cosa - cosb)(cosa + cosb) + sina - sinb)(sina - ...
August 19, 2016

Maths Algebra
3(5x-7)-2(9x-11)=4(8x-13)-17 15x - 21 - 18x + 22 = 32x - 52 - 17 -35x = -70 x = 2 check: LS = 3(10-7) - 2(18-11) = 9 - 14 = -5 RS = 4(16-13) - 17 = 12 - 17 = -5 my answer is correct
August 19, 2016

Maths Squares and Square roots
The sum cannot be found without some kind of addition somewhere, but .... look at the last one: add the first and last ---> 22 add the 2nd and 2nd last ---> 22 add the 3rd and 3rd last ----> 22 how such pairs of 22 can you find? If you have an odd number of terms, do ...
August 19, 2016

Maths Triangles
Too messy to type here. That proof should be in most textbooks, if not, Google it. https://search.yahoo.com/search?fr=spigot-nt-gcmac&ei=utf-8&ilc=12&type=692858&p=proof%20:%20sum%20of%20angles%20in%20a%20triangle%20equals%20180
August 19, 2016

Maths Quadrilaterals
Once you have proven that the sum of the angles in a triangle is 180° ..... in your quad, draw in any diagonal to create two triangles. So ......
August 19, 2016

Maths Time and Work
Poorly worded. By "rates of working" , do you mean the amount of work done, or the time taken to do the same job.
August 19, 2016

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

  1. Pages:
  2. <<Prev
  3. 1
  4. 2
  5. 3
  6. 4
  7. 5
  8. 6
  9. 7
  10. 8
  11. 9
  12. 10
  13. 11
  14. 12
  15. 13
  16. 14
  17. 15
  18. Next>>