Friday
April 18, 2014

Posts by Reiny


Total # Posts: 26,007

math
Lexi's amount --- x Maria's amount --- 250-x Lexi spent 2/5 of x, so she has 3x/5 left Maria spends 40, so she has 250-x-40 or 210-x left 3x/5 = 210-x times 5 to get rid of fractions 3x = 1050 - 5x 8x = 1050 x =131.25 So Lexi had $131.25 and Maria had 118.75 check: Lex...

Pre calculus
cos(Ø - 42°) = -1 I know cos 180° = -1 Ø - 42 = 180 Ø = 222° , only one solution between 0° and 360° (look at the graph of cos Ø ) The period of cos(Ø-42) is 360° so a general solution is Ø = 222° + 360k°...

math
I did this for you on Tuesday. http://www.jiskha.com/display.cgi?id=1384305313 What part of my solution did you not like ?

interest math
How are you getting your answers ??? a) interest = 5000(.09)(80/365) = 98.63 b) value = 5000 + 98.63 = $5098.63 c) look at a calendar, count 80 days starting April 13 as one, april 14 as 2 , etc

interest math
I am assuming you are using the standard compound interest method, simple interest is seldom used for periods longer than a year 8000(1.0525)^n = 10100 1.0525^n = 1.2625 n log 1.0525 = log 1.2625 n = 4.5554 years , assuming the rate is 5.25 per annum compounded annually at con...

math
number of games = C(6,2) = 6(5)/2 = 15

Math
8+6+x = 28 x = 14 HOWEVER, such a triangle is not possible, since the sum of any two sides must be greater than the third side, and 8+6 is not greater than 14

math
volume of first = 1.5(1.5)(.25) = .5625 cubic inches volume of last = 3.25(3.5)(.25) = 2.84375 2.84375/.5625 = 5.055.. = 505.6%

Math help please
1. assuming the 12 points were scored by 2 touchdowns, (could have been 4 fieldgoals) and n is the total number of touchdowns scored, it would be A(n) = 12 + 6(n-2) , .... two have already been counted if n is the number of touchdowns after the initial 12 points, it would be A...

math
let t = 0 , d(0) = 250 - 0 = 240 At the beginning the plane is 250 miles from its destination , point (0,240) let d(t) = 0 0 = 250-100t 100t=250 t = 2.5 after 2.5 hrs, the plane has reached its destination point (2.5, 0)

math
1.3(h-1) = 10 h-1 = 10/1.3 h = 10/1.3 + 1 or appr 8.69 hrs or appr 8 hrs and 41.5 minutes

rates
to go for 2 hrs at 12 km/h will take you 24 km so use a ratio: 2/t = 24/54 24t = 108 t = 108/24 hrs or 4.5 hrs

Math
0.000027 ÷ 0.000009 = 2.7 x 10^-5 ÷ 9.0 x 10^-6 = (2.7/9) x 10^(-5 - (-6)) = .3 x 10^1 = 3

math
The radius of the fence would be 20 ft circumf = 2πr = 2π(20) = 40π or appr 125.66 so I guess B comes closest

rates
In 3 hrs, it flies 180 km, so in 1 hour , it flies 60 km then in 4 hrs, it would fly 4(60) or 240 km

Math
Assuming this is on earth and the rocket goes up vertically, d = -16t^2 + 120t + 4 dd/dt = velocity = -32t + 120 when does it hit the ground? 0 = -16t^2 + 120t + 4 4t^2 - 30t - 1 = 0 t = (30 ± √916)/8 = 7.5332 or a negative which we'll reject velocity = -32(7....

Math-Probability
1. prob = (1/6)(1/6) = 1/36 2. the colour does not matter there are 4 ways to get a sum of 5 (1,4) (2,3) (3,2) (4,1) prob = 4/36 = 1/9 3. Again, what does the colour have to do with it? prog(no 6 showing) = (5/6)(5/6) = 25/36 prob(at least one 6) = 1 - 25/36 = 11/36

Math-Probability
could be RRR , WWW, or BBB prob = (8/20)(7/19)(6/18) + (5/20)(4/19)(3/(18) + (7/20)(6/19)(5/18) = 336/6840 + 60/6840 + 210/6840 = 606/6840 = 101/1140

Math--PLEASE HELP!!!
10 cases for 1st draw, 10 for the 2nd, 10 for the third, 10 for the 4th prob = 1/10^4 = 1/10000 if ball is not returned prob = 1/(10*9*8*7) = 1/5040

Finite
first find prob that they are all white = (5/9)(4/8)(3/7) = 5/42 so prob that at least one is black = 1 - 5/42 = 37/42 = .881

Pre-Calculus
Before I attempt this ..... I am curious why you would put a coefficient of 1 in front of the variables, such as in (1x + 2y) and (1xy) At this stage of Calculus, they would certainly be understood and not needed. I am tempted to guess you meant (1/x + 2y) and √(1/xy) pl...

math
I have no clue how you got your answer, but did you think about the validity of your answer? A city 6503 miles high would put it in a pretty high orbit. The space station is only about 230 miles high. 11.35 = 14.7 e^(-.21a) .7721088.. = e^(-.21a) -.21a ln e = ln .7721088.. a =...

math
Thought this looked familar. Just change the numbers a bit http://www.jiskha.com/display.cgi?id=1384227123

math
just expand it, and simplify y = (x-7)^2 - 5 y = x^2 - 14x +49 - 5 y = x^2 - 14x + 44 you do the 2nd one, let me know what you got.

MATH HELP
just change the coefficient of the binomial squared e.g#1 : y = 5(x-3)^2 + 2 e.g.#2 : y = -123(x-3)^2 + 2

Math
to type an exponent, we use the ^ a) y = (x-7)^2 + 4 vertex is (7,4) you must learn the pattern to pick out the vertex from that standard form if y = a(x-p)^2 + q, the vertex is (p,q) (notice the x value is opposite of p, the y value is the same as q )

Algebra 1 (Reiny or Kuai)
correct,

math
I will assume that 5x means "5 times " Sam --- x Julius --- 5x x + 5x = 78 6x = 78 x = 13 julius sold 5(13) or 65 computers what does WRIING stand for ?

Algebra 1 (Reiny or Kuai)
#1. p(1+4) - 2(p+6) = 6 5p - 2p - 12 = 6 3p = 18 p = 3 the 2nd question is correct, the point is NOT on the line

Math (ms sue or Kuai pleas e help)
let's work in feet (hate this non-metric stuff) 1 mile = 5280 ft let the width be x then the length is x+5280 area = x(x+5280) 1 acre = 43560 ft^2 then 7680 acres = 334540800 ft^2 x^2 + 5280x = 334540800 complete the square ... x^2 + 5280x + 6969600 = 334540800+6969600 (x+...

math
can't tell who lines up with what.

Math
consider the first term to be .7(1) = .7 term 2 = .7^2 = .49 what term = .01 .7^n = .01 n ln .7 = ln .01 n = ln.01/ln.7 = 12.9 term 12 = .7^12 = .0138 > .01 term 13 = .7^13 = .00968 < .01

Math
part 1 No idea, since you didn't tell us what he paid for them part 2 So he had 35% of the 500 oranges left or 175 of those 8% went bad so he still had 92% of the 175 to sell or 161 return per orange = 24.15/161 = .15 he sold them at 15 cents each ( good price, must be an ...

Algebra 2
Since you are to use the quadratic formula .... x = (-9 ± √(81 - 4(5)(-2))/10 = (-9 ± √121)/10 = (-9 ± 11)/10 = 2 or -1/5

math
work backwards since they "doubled" every 12 hours ... (1/2 day = 12 hours) at end of 2 days -- 48 at end of 1.5 days -- 24 at end of 1 day -- 12 at end of 1/2 day -- 6 at start ----------- 3

Trig
The magnitude of the resultant R is R^2 = 650^2 + 300^2 R = appr 715.89 if Ø is the angle it makes with the longer vector, then tanØ = 300/650 = ... Ø = appr 24.8°

objection - U.S. and Global Economics: Involving MATH
Ms Sue used the concept of simple interest. This is a longterm annuity type question and has to be done with compound interest. i = .055/12 = .0045833.... , n = 12(30) = 360 let the monthly payment be P 250000 = P( 1 - 1.00458333...^-360)/.00458333.. P = 1419.47

For keri - math help please
I have noticed your post many times now, and you are probably wondering why nobody is answering it. Personally I am not familiar with the king of mathematics you are dealing with. I have no idea what the "lifo method" is. Secondly, I am not in the US, so I am not fam...

Trigonometry - Identities and proof
Two of the standard conversion formulas are: sinA - sinB = 2sin((A-B)/2) cos( (A+B)/2) and cosA - cosB = - 2sin( (A-B)/2) sin( (A+B)/2) see: near bottom of page under: Sum-to-Product Formulas http://www.sosmath.com/trig/Trig5/trig5/trig5.html RS = -(sinx - siny)/(cosx - cosy) ...

or - Pre-Calculus
D^2 = (x^2 + 8x + 12) 2D dD/dt = 2x dx/dt + 8 dx/dt dD/dt = dx/dt (2x+8)/2D dD/dt = dx/dt (x+4) / √(x^2 + 8x + 12)

Precalculus 12
t^4-20t^3-20t^2+1500t+15000 = 24000 t^4-20t^3-20t^2+1500t - 9000 = 0 There is no practical easy way to solve this equation, Newton's method would be my way. I sent it through Wolfram and got http://www.wolframalpha.com/input/?i=t%5E4-20t%5E3-20t%5E2%2B1500t+-+9000+%3D+0 no...

College Level Calculus
number of extra trees per acre --- n number of trees per acre = 20+n yield per tree = 720 - 15n number of oranges = N = (20+n)(720-15n) = 14400 + 420n - 15n^2 N ' = 420 - 30n = 0 for a max of N 30n = 420 n = 14 for the best yield there should be 20+14 or 34 trees per acre

Algebra
the slope of the new line must be -9/7 so equation is: y-2 = (-9/7)(x+1) 7y -14 = -9x - 9 9x + 7y = 5 ------ A You even said that you knew the slope had to be negative (true), so why did you use a positive slope ???

Correction - Math
Magnus is not correct 2000(2000^2000) = 2000^2001 This number is unimaginably huge. e.g. 2000^1 has 4 digits 2000^2 has 7 digits 2000^3 has 10 digits 2000^4 has 14 digits for each increase of 4 in the exponent there are 10 extra digits in the answer. 2001/4 = appr 500 so there...

algebra
each rotation covers 90/45 m or 2 m circumf = πd πd = 2 d = 2/π m

motion problem
rate of paddling in still water ---- x km/h speed of the river -------------- y km/h x-y = 6 x = y+6 distance uprstream = 6(10) = 60 km distance downstream = 4(x+y) = 4(y+6 + y) = 8y + 24 8y + 24 = 60 y = 4.5 x = 10.5 Actually I did a lot of extra work. The question was , how ...

matth
done, check earlier post

math
charge for first 25 songs --- x dollars per song charge for songs over 25 ---- y dollars per song 25x + 3y = 34.8 25x + 5y = 40.7 subtract the 1st from the 2nd 2y = 5.9 y = $2.95 sub into the 1st 25x + 3(2.95) = 34.8 25x = 25.95 x = $1.04

algebra
For the x-intercept, let y = 0 (put your pinkie finger over the y term and mentally solve what is left of the equation.) I see 5x = -2 , so x = -2/5 Of course we let y = 0, so the point is (-2/5, 0)

Algebra
see the solution I gave to your other problem which is similar to this one.

Algebra
complex roots always come in conjugate pairs so roots are 9, 3 ± 5i, ± 9i fo f(x) = (x-9)(x-3-5i)(x-3+5i)(x+9i)x-9i) = (x-9)(x^2 - 6x + 34)(x^2 + 91) expand if need be

Math... PLEASE HELP!!
2n-4 = 42 2n = 46 n = 23 you are correct

Math
prob of getting one black from 1st box = 3/4 prob of getting one black from 2nd box = 6/8 = 3/4 mmmmmhhhh? prob(2 blacks from 1st) = (3/4)(2/3) = 1/2 prob(2 blacks from 2nd) = (6/8)(5/7) = 15/28 mmmh again!

geometry
centre is at (9,0), radius = √484 or 22 (use ^ to indicate an exponent such as (x-9)^2 + y^2 = 484

GEOMETRY
Think of laying out the 3 given sides in a straight line to get a sum of 2011+2012+2013 = 2036 As long as x is < 2036 you will be able to "kink" the 3 lines at their joints and form a quad. If x = 2036, they will all lie on a straight line. if x > 2036, you can...

GEOMETRY
Think of laying out the 3 given sides in a straight line to get a sum of 2011+2012+2013 = 2036 As long as x is < 2036 you will be able to "kink" the 3 lines at their joints and form a quad. If x = 2036, they will all lie on a straight line. if x > 2036, you can...

Math
let h(t) be the position function h(t) = - 16t^2 + 120t + 4 . you had that. when it hits the ground, h(t) = 0 -16t^2 + 120t + 4 = 0 4t^2 - 30t -1 = 0 solve with quadratic formula t = (30 ± √916)/8 = 7.533 or a negative value of t it will hit the ground after appr ...

math
In your previous post of this same question, I showed you that this equation has no answer. Since you posted this new one after I posted my reply, you did not even look at it. Clearly you have some type of typo or the question is bogus.

algebra
2w + 36 + 2w = 2w + 36 - 12 + 2w + 6 0 = -6 A false statement, so .... no solution

algebra
you are solving 12.17 = 14.7 e^(-.21a) .827891156 = e^(-.21a) ln (.827891156) = -.21a lne -.21a = -.188873... a = appr .8994 miles or appr 4750 ft to the nearest ten feet.

Calculus
let the ladder be y ft above the ground x^2 + y^2 = 15^2 when foot is x ft from wall y^2 = 225-x^2 y = (225-x^2)^(1/2) 2x dx/dt + 2y dy/dt = 0 dy/dt = -2x dx/dt/(2y) = (-x dx/dt)/y = -2x(1/2)x/√(225 - x^2) = -x^2/√(225-x^2)

math
2x/5 > 2/1 2x > 10 x > 10 and 2x/5 < 3/1 2x < 15 x < 7.5 so x < 7.5 AND x > 10 no such number exists. your answer of x = 2.4 test: if x=2.4 4.8/5 = .96 which < 3 BUT NOT > 2

Math
you left out the exponent 3x^ ????

Check my CALCULUS work, please! :)
#1 and #2 are correct #3 --- here is a neat trick that works for most limit questions. Use your calculator and try a number close to your approach value e.g. for #1 I used h = .001 and then evaluated the expression for #3, try a "large" number. However for this one e...

math
each of the friends gets 7/4 lbs or 1.75 lbs two of those combined is 2(1.75) or 3.5 lbs go to the food pantry. Audrey used 1 2/3 of the food pantry apples to make apple pies she used (5/3)of 3.5 or (5/3)(14/4) = 35/6 lbs or appr 5.83 lbs

algebra
so the new line has slope -5/2 You should memorize that the slope of Ax + By = C is -A/B I see only one equation where -A/B = -5/2

algebra
y = 5 or y = 0x + 5 is a horizontal line with slope of 0 Thus a perpendicular line would be a vertical line, which has an undefined slope. Any vertical line has the form x = k , where k is a constant

algebra 2
I am assuming you are factoring ? for x^2 - 19x + 72 there are no factors with rational numbers (I found the discriminant b^2 - 4ac to be 649, which is not a perfect square, thus no factors) x^2 - 25x - 90 same thing, b^2-4ac = 985 , no factors I assume a typo in the 3rd and y...

algebra
I agree, B is the correct choice.

Algebra
bitte schön

Algebra
slope of the given equation is 7/12 the only one in your choices with a slope of 7/12 is C

Pre-algebra
Since it is perpendicular its slope must be +1 equation: y = x + b but (-2,-2) lies on it, so -2 = -2+b b = 0 the new equation is y = x

Math
cosx = 2cos^2 x - 1 2cos^2 x - cosx - 1 = 0 (2cosx + 1)(cosx - 1) = 0 cosx = -1/2 or cosx = 1 x = 120° or 240° or x = 0 or x = 360° Those are not "points of intersection" , they are solutions to your equation. You can't find points of intersection, si...

Math
assuming the ground level below the cliff to be zero I would say: h(t) = -16t^2 + 16t + 96

algebra
I will assume you meant: (2b-2)/(2b^2 - 8) = 2(b-1)/( 2(b^2 - 4) = (b-1)/(b^2 - 4)

PreCal
(1+2√3)(2 - 3√-3 ) =2 - 3√-3 + 4√3 - 6√-9 = 2 - 3√3i + 4√3 - 18i you had that , but they probably want it this way (2+4√3) - i(3√3+18) or (2+4√3) + (-3√3 - 18)i where a = 2+4√3 b = -3√3 - 18

Probability
done for you here: http://www.jiskha.com/display.cgi?id=1384037252

Calculus
x-intercepts, let y = 0 .005x + 25 + 180/x = 0 ,005x^2 + 25x + 180 = 0 x = (-25 ± √621.4)/.1 = appr -.721 or -499.28 y-intercepts, let x = 0 y = undefined, there is no y-intercept dy/dx = .05+0-180/x^2 = 0 for max/min .05 = 180/x^2 x^2 = 3600 x = ± 60 plug ...

Algebra
To raise the water level 1 foot took 44 minutes so to raise it 2.75 ft will take 44(2.75) or 121 minutes or 2:01 hrs since she started at 8:15 it will be 2 3/4 ft deep at 8:15 + 2:01 or at 10:16

geometry PLEASE
Going back to your previous posts, I did read #5 carefully when you posted these before. At the end you said "an equilateral circumscribed about the same circle" I can only interpret that as "an equilateral triangle circumscribed about the same circle", and...

Math
I will do #1 #1 let R represent picking a raspberry, N a non-raspberry 12R , 14N a) so you want: NNRNRN prob = (14/26)(13/25)(12/24)(12/23)(11/22)(11/21) = .01913 Prob(none cheese)= (18*17*16*15*14*13)/(26*25*24*23*22*21) = .08063 at least one cheese = 1 - .08063 = .91936

algebra 1
most texts use these definitions: y intercept - slope form : y = mx + b standard form: Ax + By = C general form : Ax + By + C = 0 so you want the x and y terms on one side, the constant on the other side y - 8 = 2(x+3) y - 8 = 2x + 6 2x + 6 = y - 8 2x - y = -14 , looks like C

Steve is right - Maths
Steve is right, it is a cycle of 3 terms, not 4 terms like I hastily concluded. so -25/22

Maths
A1 = 22/47 A2 = (22/47 - 1)/(22/47 = -25/22 A3 = (-25/22 - 1)/(-25/22) = 47/25 A4 = (47/25 - 1)/(47/25) = 22/47 A5 = -25/22 A6 = 47/25 A7 = 22/47 ... looks like if the subscript is divisible by 4, the answer is 22/47 since 2012 divides evenly by 4, we get 22/47 as a/b, so a = ...

Algebra 1
y---->7y would "stretch" it by a factor of 7 y ---- -7y would not only stretch it but also reflect it in the x-axis. so it looks like D after your correction of the wording

Rachel, Kim .. Cabdy
This is silly. Within about 3 minutes, you have managed to post the same question 6 times under a different name. When you decide who you are and become a bit more patient, I will attempt your question. In the meantime, where does your difficulty come in?

GEOMETRY URGENT PLEASE
I did #5 for you on Thursday. http://www.jiskha.com/display.cgi?id=1383829501 Did you not look at it ? for the above, it says" your image has been removed"

statistics
Assuming you want to be above 1.75, yes you are correct http://davidmlane.com/hyperstat/z_table.html enter 1.75 in "above" to get 0.0401

math
trying x = ±1, ±2, ± 7, ±1/5, ±2/5, ±7/5 I found f(2) = 0 and f(x) = (x-2)(5x^3 - x^2 - 35x + 7) = (x-2)g(x) x = ±7 didn't work in the first, so it certainly will not work in this one so try x = 1/5 in the cubic factor g(1/5...

algebra
The problem is the slope. All the options indicate a slope of -3, but you stated the slope to be +3 Kuai's solution is correct according to the data supplied.

Precalc
I corrected your typo sin(2x)*sinx/2cosx + cos^2 x = 1 LS = 2sinxcosx(sinx)/(2cosx) + cos^2x = sinx(sinx) + cos^2 x = sin^2 x + cos^2 x = 1 = RS

maths
According to actuarial math, where interest is considered, he paid $7640, (you cannot simply add "monies" that are in different time slots on a time graph. e.g. Making $40,000 in 1985 ≠ $40,000 in 2013 If you ignore interest the total he paid = .2(7640) + 36(19...

or - math
avoiding some of those fractions let the sides of one rectangle be x and x+1 and the other, y and y+1 4x+2 + 4y+2 = 36 x+y=8 y = 8-x area = A = x(x+1) + y(y+1) = x^2 + x + y^2 + y = x^2 + x + 64-16x+x^2 + 8-x = 2x^2 - 16x + 72 Quadratic opening up, so a minimum dA/dx = 4x - 16...

statistics
great webpage for your problem, just plug in the values that you have http://davidmlane.com/hyperstat/z_table.html

Calculus!!!
if f ''(x) = 8 + x^3 + x^5 , notice how we write exponents then f' (x) = 8x +(1/4)x^4 + (1/6)x^6 + C f(x) = 4x^2 + (1/20)x^5 + (1/42)x^7 + Cx + D

Algebra 1
number of quarters= x number of dimes = y number of pennies =8-x-y value: 25x + 10y + 1(8-x-y) = 83 24x+ 9y = 75 9y = 75 - 24x 3y = 25 - 8x 25 -8x must be a positive multiple of 3 so clearly x can only be 1 , 2, or 3 of those only x = 2 will work if x = 2 3y = 25-16 = 9 y = 3 ...

Algebra
good job

Algebra
You are welcome, did you get the 2nd question?

Algebra
number of nickels = 3x number of dimes = 8x number of quarters = x value of the money = 5(3x) + 10(8x) + 25x = 120x number of coins = 12x suppose we have 12x dimes as stated value of all the those 12x dimes = 10(12x) = 120x so 120x = 120x 0 = 0 !!!!! the variables dropped out ...

algebra
suppose you have an equation in standard form e.g. 4x - 5y - 8 = 0 step 1. "move" all terms except the y term to the other side -5y = -4x + 8 step 2. divide each term by the coefficient of the y term -5y/-5 = -4x/-5 + 8/-5 y = (4/5)x - 8/5 all it takes is 2 steps

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