Tuesday
September 1, 2015

Posts by Reiny


Total # Posts: 30,693

PS - Math
I sure hope that the above is not how "they" are teaching you to calculate simple interest
August 7, 2015

Math
I = k(P)(T) , compare with I = PRT, so k is jus like the rate R given: when P = 3000, T=6, then I = 1260 1260 = k(3000)(6 k = 1260/( (3000)(6) ) = .07 , mmhhh, looks like we just found the interest rate I = .07(P)(T) so for the last part I = .07(3000)(7) = 1470
August 7, 2015

Math
I = k (1/d^2) given: when I = 70, d = 5 70 = k/25 k = 1750 so I = 1750/d^2 when d = 4 I = 1750/4^2 = 109.375
August 7, 2015

Math
R = k(1/T) = k/T when R = 60, T = 8 60 = k/8 k = 480 R = 480/T so when T = 6 R = 480/6 = 80 mph
August 7, 2015

Mth 156
x(1.015)^24 = 35000 x = 24484.04
August 7, 2015

math
correct
August 7, 2015

Math-manipulation of the formula
(1+i)^n = A/P 1+i = (A/P)^(1/n) i = (A/P)^(1/n) - 1
August 7, 2015

math
shorter of the other sides --- x longer of the other sides ---- 2x To be a triangle the sum of any two sides must be greater than the third side x+2x > 17 AND x+17>2x AND 2x+17>x 3x > 17 AND x < 17 AND x > -17 x > 17/3 AND x < 17 (x is between 5.666.. ...
August 6, 2015

oops - math
I have to read the question more carefully. It clearly said 10 months and I used 12 months so let's just make a simple change (1+i)^10 = 1.15625 take the 10th root 1+i = 1.15625^(1/10) 1+i = 1.014624.. i = .014624 annual rate = 12(.014624) = .1755 or appr 17.55%
August 6, 2015

math
let the monthly rate be i 3200(1+i)^12 = 3700 (1+i)^12 = 1.15625 take 12th root 1+i = 1.01217.. i = .01217.. annual rate compounded monthly = .14606 or appr 14.6%
August 6, 2015

algebra
(73+x)/2 = 81 73+x = 162 x = 89
August 6, 2015

Calculus 1
For you to say that you have no clue how to start this straightforward question is not a good sign if you are in a Calculus course. by Calculus, take vertical discs of width dx and height 2x+1 V = π ∫ r^2 dx V = π∫(2x+1)^2 dx from 0 to 1 = π [ (1/6)(...
August 6, 2015

math
first of all, for a + 1/a to be equal to 6, a would not be a "nice" number we could find it .... a + 1/a = 6 multiply each term by a a^2 + 1 = 6a a^2 - 6a + 1 = 0 a = (6 ± √32)/2 = 3 ± 2√2 , not nice as predicted we could square that, and ...
August 6, 2015

math
I will assume you mean 2003^(x^2 + 2x - 35) = 1 then 2003^(x^2 + 2x - 35) = 2003^0 thus: x^2 + 2x - 35 = 0 (x+7)(x-5) = 0 x = -7 or x = 5 and the product of those two x's is -35
August 6, 2015

math
if 3^a = 2 then 9^(4a) = (3^2)^(4a) = (3^a)^8 = 2^8 49^(2b) = (7^2)^(2b) = (7^b)^(4) = 5^8 then 9^4a * 49^2b = (2^8)(5^4) ------> C
August 6, 2015

math
I can only see (0,5) and (-5,0) the right side has to be a perfect cube so it could be 1,8,27,64,125, 216 which means that a^3 + 125 must be one of those numbers, and a^3 would be one of those : 124, 117, 98, ... does not look too promising other than the 2 I stated
August 6, 2015

Trigonometry
make your sketch drop an altitude from the plane to the ground to get 2 right-angled triangles let the height of the plane be h let the base of the 11° triangle be x then the base of the other triangle is 2-x from the 11° triangle: tan11 = h/x --->h = xtan11 from ...
August 5, 2015

algebra
volume = x(x+2)(x+6) expand it, if there is need to do so.
August 5, 2015

statistic
This webpage is perfect for your type of question. Just enter the data http://davidmlane.com/hyperstat/z_table.html
August 5, 2015

Math
short side --- x diagonal --- x+8 other side --- y x^2 + y^2 = (x+8)^2 x^2 + y^2 = x^2 + 16x + 64 y^2 = 16x + 64 y = √(16x+64) area = xy = 60 x√(16x+64) = 60 square both sides x^2(16x+64) = 3600 16x^3 + 64x^2=3600 x^3 + 4x^2 - 225 = 0 looks like x = 5 works then y...
August 5, 2015

Math
yes
August 5, 2015

alg1
8m^2 +20m=12 8m^2 +20m-12=0 divide each term by 4 2m^2 + 5m - 3 = 0 (2m - 1)(n + 3) = 0 m = 1/2 or m = -3
August 5, 2015

math
The lengths of the arms or rays that form an angle have nothing to do with the size of the angle they form e.g. sketch any angle. Now extend the rays that form the angle. Did anything happen to the angle ??
August 5, 2015

maths
anonymous made the "lucky" assumption that the second fraction ?/x^2 had a constant for a numerator. In general you cannot make such an assumption. If the denominator is a second degree expression, like x^2, then the numerator could be a first degree expression of ...
August 5, 2015

maths
You fixed Damon's concern, but still brackets are missing I will assume you meant: (x^3+6)/(x^2(x+3) ) I first did a long algebraic division to get it to 1 - (3x^2 - 6)/(x^2(x+3) ) So let's just work on that last term let (3x^2 - 6)/(x^2(x+3) ) = A/x + (Bx + C)/x^2 + D...
August 5, 2015

mathematical
Now: father ---- x Robin ---- x-25 after 10 years: father = x+10 Robin = x-25 + 10 = x-15 (x-15)/(x+10) = 1/2 2x - 30 = x+10 x = 40 state your conclusion
August 5, 2015

math
Saw this same question the other day. Is there a reason why you are using square brackets and round brackets? Is it simply (428)(-23)+(-428)(-223) ? If so, I am sure you have a calculator. remember for the order of operation, the multiplication has to be done before the addion.
August 5, 2015

Calculus
dy/dx = 2x which is the slope of the tangent at any point (x,y) on the parabola so at (1,2) , the slope of the tangent is 2(1) = 2 since the normal is perpendicular to the tangent, the slope of the normal must be -1/2 equation: y-2 = (-1/2)(x-1) you can doctor that up any way ...
August 5, 2015

Calculus
did this one yesterday http://www.jiskha.com/display.cgi?id=1438682725
August 4, 2015

Algebra
you will need a slope of -1/m so clearly false.
August 4, 2015

Calculus
x = 3 and y^2 = 12x intersect at (3,6) and (3,-6) so we can take horizontal slices, and because of the symmetry just go from y = 0 to y = 6 and double the result. we also have a radius of 3 - y^2/12 V = 2π ∫r^2 dy from 0 to 6 = 2π ∫(3 - y^2/12)^2 dy from ...
August 4, 2015

calculus
assuming a = -32 and seeing that the initial velocity was -15 from a height of 904, I know s = -16r^2 - 15t + 904 we want s = 0 16t^2 + 15t - 904 = 0 won't waste time trying to factor it ... t = (-15 ± √58081)/32 = (-15 ± 241)/32 ----- ahh, it does ...
August 4, 2015

calculus
welcome, hope you checked my arithmetic
August 4, 2015

calculus
ok, then a = t^(-3/2) v = -2 t^(-1/2) + c s = -4 t^(1/2) + ct + k case1: s=8, when t = 1 8 = -4 + c + k 12 = c + k case2: s = 16, when t = 4 16 = -4(2) + 4c + k 24 = 4c + k subtract them: 12 = 3c c = 4 back in 12 = c+k 12 = 4+k k = 8 then v = -2/√t + 4 when t = 9 v = -2/...
August 4, 2015

calculus
do we have a = 1/(t√t) or is it a = (1/t)√t ??
August 4, 2015

Probability
Consider the elf and the dwarf as one item, so you are now arranging 4 which is 4! or 24 but we can switch the elf and the dwarf and still have them side by side, so 2(4!) = 48
August 4, 2015

math
so the year can't have any zeros smallest possibe = 1911 largest is 1999 since they all have to start with 99, variations of products can only come from the last 2 digits 1914 1941 1922 all produce the same product 1942 1924 1918 1981 all produce the same product same ...
August 4, 2015

math
look for an exception, that way we can rule out the choice which does not work e.g. x = 500 √516 = appr 22.7 A) is 22.7 between 22.36 and 22.38 , no B) is 22.7 between 22.38 and 22.4 , no I will stop here, since the question does not make any sense to me no matter what ...
August 4, 2015

math
smallest n = 2 n = 2 ---> 2,4,6 nope n = 3 ---> 3,5,7 YES n = 5 ---> 5,7,9 nope n = 7 ---> 7,9,11 nope n = 11 ---> 11,13,15 nope .. n = 23 --> 23, 25, 27, nope Other than 2, all primes are odd so we need 3 sequential odd numbers to have the above property BUT...
August 4, 2015

math
(±3,±4) that's 4 of them (±4,±3) that's 4 more (0,±5) 2 more (±5,o) and 2 more I count 12
August 4, 2015

Calculus
V = π integral [sin^2 (ex) ] dx from 0 to ln π = π ( x/2 - (1/(4e)) sin(2ex) ) from 0 to ln π = π (ln π/2 - 1/(4e) sin(2e ln π) - (0 - 0) = 1.815 How can you get 2 answers?
August 4, 2015

Math
speed on first way --- x speed on return ---- x-30 time for first part = 60/x time for other part = 60/(x-30) total time = 60/x + 60/(x-30) = (60(x-30) + 60x)/(x(x-30) = (60x - 1800 + 60x)/(x-30) =120(x - 15)/(x(x-30) avg speed = 120/(120(x - 15)/(x(x-30) ) = 120x(x-30)/(120(x...
August 4, 2015

math
ok, that is not a good idea. How about this.... let Sum(n) denote the sum of n terms, sum(1) = 1/2 sum(2) = 1/2 + 1/6 = 4/6 = 2/3 sum(3) = 2/3 + 1/12 = 9/12 = 3/4 sum(4) = 3/4 + 1/20 = 16/20 = 4/5 notice any pattern yet ??? let's do one more sum(5) = 4/5 + 1/30 = 25/30 = 5...
August 4, 2015

math
How are you doing it? Perhaps you are doing it the fastest way. What is your choice of answers?
August 4, 2015

math
p(1 - 1.004^-360)/.004 = 250000 solve for p let me know what you got
August 4, 2015

8th grade
you must have the formula in front of you, either from your notes or your texbook sub in the point (-3,-2) and the value of the slope and compare the result with the choices given. It should be obvious.
August 4, 2015

math trig
6sinxcosx - 3sinx = 2 - 4cosx 3sinx(2cosx - 1) = 2(1 - 2cosx) 3sinx(2cosx - 1) - 2(1 - 2cosx) = 0 3sinx(2cosx - 1) + 2(2cosx - 1) (2cosx - 1)(3sinx + 2) = 0 cosx = 1/2 x = 60° or 300° or 3sinx = -2 sinx = -2/3, so x is in III or IV from my calculator, sin 41.81°...
August 4, 2015

Calculus
I will assume you meant: x = 4 - y^(2/3) I assume you made a sketch let's take horizontal slices .... the y-intercept is (0,8) so the region is not closed. I will assume you want the region between the x-axis and and the y-axis area = ∫4 - y^(2/3) dy from 0 to 8 = 4y...
August 4, 2015

Urgent math
again ... http://www.jiskha.com/display.cgi?id=1438656557
August 4, 2015

Math
done here http://www.jiskha.com/display.cgi?id=1438656557
August 4, 2015

arithmetic sequence
"the 40th term of an arithmetic sequence is equal to the sum of the 20th and 31st term" ----> a + 39d = a+19d + a+30d a = -10d but d = -10 a = 100 the first term is 100
August 4, 2015

math algebra
let the number of wings be x cost of wings = .30x cost of sauce = .01x for a total of .31x (yes, you are right we can just say 1 wing costs 31 cents) so (.31x + 7.50 + 2.50)(1.085)(1.15) ≤ 60 take it from there ( got 120 wings, assuming you are buying wings in multiples ...
August 3, 2015

math
how did you get that ?? 2.5x + 2.8(480-x) = 2.68(480) 2.5x + 1344 - 2.8x = 128.40 -.3x = -57.6 x = 192 so he should use 192 pounds of the $2.50 and 288 pounds of the $2.80 stuff check: cost of the parts = 2.5(192) + 2.8(288) = 1286.40 cost of the mix = 2.68(480) = 1286.40 my ...
August 3, 2015

math
let the $2.50 stuff be x solve for x 2.5x + 2.8(480-x) = 2.68(480)
August 3, 2015

Math
let the angle be x then it's complement = 90-x and it's supplement is 180-x 180-x = 11(90-x) 180-x = 990 - 11x 10x = 810 x = 81
August 3, 2015

math
make a sketch of a line with equal intercepts, e.g. (a,0) and (0,a) slope = (a-0)/(0-a) = -1
August 3, 2015

Math
jack's rate = 1/6 Jerry's rate = 1/x combined rate = 1/6 + 1/x = (x+6)/(6x) given: 1/( (x+6)/(6x) ) = 4 6x/(x+6) = 4 6x = 4x + 24 2x = 24 x = 12 It would take Jerry to work 12 alone to do the job check: combined rate = 1/6 + 1/12 = 3/12 = 1/4 time at combined rate = 1...
August 3, 2015

calc
F(x) = ∫(2t + 4) dt from 2 to x = t^2 + t | from 2 to x = x^2 + x - (4 + 2) = x^2 + x - 6
August 3, 2015

math
Welcome Ms Sue, :)
August 3, 2015

math
The time is inversely proportional to the number of ants, that is, as the number of ants increase, the time needed to build the anthill decreases time = k/ants if time = 5, ants = 1000 5 = k/1000 k = 5000 time = 5000/ants time = 5000/2500 time = 2 hrs or simply as an inverse ...
August 3, 2015

Algebra ASAP
A(t) = 17000(1.051)^t b) i = .051/365 A(t) = 17000(1 + .051/365)^(1095) = $19810.31 continuous ... 20000 = 17000 e^(.051t) solve for t (I got 3.1866)
August 3, 2015

Algebra ASAP
since half-life is given, use 1/2 as a base so m(t) = 6 (1/2)^(t/10), where t is number of seconds b) using base e ..... m(t) = 6 e^(kt), where k is a constant We have to find k given, when t = 10, m(10) = 3 3 = 6 e^(10k) .5 = e^(10k) ln .5 = 10k k = -.069315 m(t) = 6 e^(-....
August 3, 2015

Algebra
I am going out on a limb here and assume you meant: 5^( (x-2)/4) = √5 5^( (x-2)/4) = 5^(1/2) (x-2)/4 = 1/2 x-2 = 2 x = 4 The way you typed it .... 5^x - 1/2 = √5 5^x = √5 + 1/2 x log5 = log (√5 + 1/2) x = log(√5 + 1/2) /log5 = appr .62539
August 3, 2015

Urgent math
remember we can take logs of only positive numbers, so ... domain: x> -3 range : y is any real number asymptote : x = -3
August 3, 2015

Precaculculus
you are correct. An interesting question now would be ... what is the value of 'a' ?
August 3, 2015

Math
I agree, good work
August 3, 2015

math
Why do "the wheels on a bus go round and round" ??
August 3, 2015

pre-cal
just use the formula let a = 10, so we can use your standard base 10 logs on your calculator log14 41 = log 41/log 14 = appr 1.407158.. = 1.407 correct to 3 decimals check by evaluating 14^1.407 on your calculator. What did you get?
August 3, 2015

Urgent math
n(t) = 19000 e^(.07t) , where t is the number of years since 2005 in 2010 , t = 5 n(5) = 19000 e(.07(5)) = 26962 use the method I showed you in your previous post do answer c)
August 3, 2015

Urgent math
general equation: number = a e^(kt) , where a is the initial amount, t is the time in hours and k is a constant. case1: when t = 2, number = 400 400 = a e^(2k) case2: when t = 6 , number = 25600 25600 = a e^(6k) divide the 2nd equation by the 1st 64 = e^(4k) 4k = ln64 k = ln64...
August 3, 2015

College Algebra
you were not quite done, 3.4 is the difference in the Richter scale values, so the relative strength of the quakes is 10^(3.4) = appr 2512 times as large remember that the Richter scale is a base 10 logarithm relationship
August 3, 2015

College Algebra
general equation amount = a (1/2)^(t/5730) , where t is in years .8 = 1 (1/2)^(t/5730) .8 = 1 (.5)^(t/5730) log .8 = (t/5730) log.5 t/5730 = log.8/log.5 t = 5730(log.8/log.5) = appr 1844.6 years
August 3, 2015

College Algebra
4 + 5^6x = 8 I will assume you meant 4 + 5^(6x) = 8 5^(6x) = 4 log both sides and use rules of logs 6x log5 = log4 x = log4/(6log5) b) x = appr .143559
August 3, 2015

stadistic
for any question, prob(correct guess) = 1/4 prob(wrong guess) = 3/4 To have exactly 7 of 15 correct, prob = C(15,7)((1/4)^7 (3/4)^8 = 6435 (1/16384)(6561/65536) = appr .039
August 2, 2015

gnmps
let their ages be 6x and 7x (6x+12)/(7x+12) = 12/13 78x + 156 = 84x + 144 -6x = -12 x = 2 they are now 12 and 14
August 2, 2015

Math ho.
You have not indicated if the given number has any repeating decimals. The way you typed it, it appears to terminate. Thus it would be rational. An irrational number has decimals than neither repeat nor terminate. The way you typed it, we can't tell.
August 2, 2015

Math ho.
nope, each length is 25/2 m which is a rational number.
August 2, 2015

Algebra
I will read that as: 4/(x^2 - 4x + 1) + 2/(x^2 - 1) We usually "solve" equations, but you have no equation. Are you simplifying? If so, I was expecting the first denominator to factor like the second one, so we can find the LCD. The way it stands, the simplification ...
August 1, 2015

MATH
I agree with Bosnian that the question contains a typo. If the sum of n terms is 225 as stated we could solve for r = 2.309.. but then the solution for n is not a whole number. Bosnian assumed correctly that sum(8) = 255
August 1, 2015

alpha
secØ = x - tanØ for a trivial solution, but .... If you want secØ in terms of x, then you have a mess Secø + tanø=x 1/cosØ + sinØ/cosØ = x (1+sinØ)/cosØ = x 1 + sinØ = xcosØ square both sides 1...
August 1, 2015

MTH 157
x(1.04)^5 = 50000
July 31, 2015

Math
first get you results to sine and cosine of x since you are in II, from your diagram, sinx = 15/17 tanx = -15/8 use the formula for tan(3x) you just found in your other post. then apply the formula for tan(A/2) actually that is a nice one: tan (A/2) = (1 - cosA)/sinA good luck
July 31, 2015

Math
easy to look up, here is one such page http://www.trans4mind.com/personal_development/mathematics/trigonometry/multipleAnglesTangent.htm If you have to actually develop it, use tan(A+B) = (tanA + tanB)/(1 - tanAtanB) on tan(3x) = tan(2x+1) after doing tan2x first.
July 31, 2015

math
let his income be x after food expenses he is left with (2/3)x he then spends (1/4+1/5)(2x/3) = (3/10)x which leaves him with 2x/3 - 3x/10 or 11x/30 (11/30)x = 1760 x = 4800 which is choice c)
July 31, 2015

math
so you want: √a + √b = √c just take any two perfect squares, add their square roots and square that to get c e.g. a = 1 , b=1, c = 4 ----> √1 + √1 = √4 a = 1 , b = 4, c = 9 a = 4, b = 9, c = 25 ---> √4 + √9 = √25 ...
July 30, 2015

math
amount of the 30% alloy to be added --- x ounces .3x + .05(10) = .2(10+x) .3x + .5 = 2 + .2x .1x = 1.5 x = 15
July 30, 2015

math
let the side of the square be x let d be the diagonal, d^2 = x^2+x^2 = 2x^2 d = √2 x "the sum of the squares of the four sides plus the sum of the squares of the two diagonals is 400" x^2+x^2+x^2+x^2 + 2(2x^2) = 400 8x^2 = 400 x^2 = 50 x = 5√2 area of ...
July 30, 2015

Probability
Is the password case sensitive ? It usually is, so number of ways to arrange 5 letters = 52^5 also assuming that letters can be repeated only one of these is correct prob(getting it right) = 1/52^5 = 1/380204032
July 30, 2015

Probability
prob(A/C) = 1/2 prob(not A/C) = 1/2 prob(that 5 out of 10 have A/C) = C(10,5)(1/2)^5 (1/2)^5 = 252 (1/2)^10 =252/1024 = 63/256 or appr .246
July 30, 2015

Probability
So he already has 1 penny, which means he can only draw another penny or another nickel Prob(as stated) = 3/8 + 2/8 = 5/8
July 30, 2015

Cones
V = (1/3)π r^2 h = 36π r^2 h = 108 Now if we cut the height in half, then the radius is also cut in half new volume = (1/3)π(r/2)^2 (h/2) = (1/24)π r^2 h = (1/24)π(108) = 9π/2 or the volume of similar solids is proportional to the cube of their ...
July 30, 2015

Math
b men earning D dollars = bD remaining men = m-b each earning D/2 so they earn D/2(m - b) = mD/2 - bD/2 total = bD + mD/2 - bD/2 = 2bD/2 + mD/2 - bD/2 , using a common denominator = bD/2 + mD/2 = D/2(b+m) , using a common factor of D/2 which is B D/2 is the same as (1/2)D
July 30, 2015

Math
It would be a good idea if you familiarize yourself with Pascal's Triangle, the 4th row has values 1 4 6 4 1 so (2x-1)^4 = (2x)^4 + 4(2x)^3 (-1) + 6(2x)^2 (-1)^2 + 4(2x) (-1)^3 + (-1)^4 the term that will yield x^2 is 6(2x)^2(-1)^2 = 24x^2 confirmed by Wolfram: http://www....
July 30, 2015

GCF
pick out the factor with the lowest exponent for each variable e.g. for the b's it would be b^5 etc
July 30, 2015

What did I did wrong MATH
number of $1 coins --- 3x number of half-dollars --- 4x Your second sentence does not make any sense to me taking your equation ... cross-multiply 9x - 18 = 4x+6 5x = 24 x = ???? , x must be a whole number Fix your second sentence.
July 30, 2015

math
I find it odd that you made the same typo in this question as somebody else did back in Nov 2014. http://www.jiskha.com/display.cgi?id=1416116940
July 30, 2015

Math
You will need brackets to establish the correct order of operations. The way you typed it, the +1 -1 would cancel and you are left with 4 /X^2 – 4x + 2/ x^2 = 4/x^2 - 4x^3/x^2 + 2/x^2 = (6 - 4x^3)/x^2 I have a strong feeling that is not what you meant.
July 30, 2015

math
I started it as a simple calculus question ... first number: x 2nd number : 48/x sum = x + 48/x d(sum)/dx = 1 - 48/x^2 = 0 for a min of sum x^2 = 48 x = √48 = appr 9 but you want the numbers to be whole numbers so possible ordered pairs: (1,48) (2,24) (3,16) (4,12) (6,8...
July 30, 2015

maths
Why not just say: the volume equals the surface area (4/3)πr^3 = 4πr^2 times 3/π 4r^3 - 12r^2 = 0 r^3 - 4r^2 = 0 r^2(r - 4) = 0 r = 0 (trivial solution) or r = 4 or the diameter is 8 Your actual question is strangely worded.
July 30, 2015

Mathematics
The zeroes of a function indicate where the corresponding graph touches or crosses the x-axis.
July 30, 2015

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