Tuesday
May 3, 2016

Posts by Reiny

Total # Posts: 34,463

math
Your decimals are not correct 0.5444444444 = .5 + .04 + .004 + .0004 + ... let's leave the .5 sitting aside for the time being. so we have .04 + .004 + ... a = .04, r = .1 sum of all = a/(1-r) = .04/(1-.1) = .04/.9 = 4/90 = 2/45 now bring in the .5 or 1/2 so 0,5444444444...
February 16, 2016

Maths
x + 10x + 100x = 1000 111x = 1000 x = 9 So by your "subtraction" after first jump : 1000-9 = 991 after 2nd jump : 991-90 = 901 after 3rd jump : 901-900 = 1 looks like he didn't quite make it.
February 16, 2016

Precal
use a ratio, C/360 = 140/210 C = 360(140/210) = ...
February 16, 2016

MATH HELP
The first part of the question is irrelevant. all we need is to compare 3.76% compounded monthly with 3.5% compounded daily let the first rate be i 1+i = (1 + .0376/12)^12 = 1.038254.. i = appr 3.825% let the second rate be j 1+j = (1 + .035/365)^365 = 1.0356.. = appr 3.56% ...
February 16, 2016

math
ar^4 = 360, but = 90 so .....
February 16, 2016

MATH HELP
credit union investment = 15000(1 + .05/365)^365 = $15,769.01 silver screen account = 20000(1 + .0525/12)^12 = 21,075.64 total after 1 year = 36,844.65 on an investment of 35,000 To make any comparison, we have to evaluate at the same "time spot". thus a) is not a ...
February 16, 2016

Trig identity inverses
go with Steve's answer, I forgot that we could pin-point the quadrant (although mine had the more-fun calculations)
February 16, 2016

Trig identity inverses
cos[cot^-1 (-√3) + sin^-1 (-1/2)] let's take it in parts cot^-1 (-√3) is the angle so that cotØ = -√3 or tanØ = -1/√3 I know tan30° = +1/√3 so Ø = 180-30 = 150° or -30° (usually we take the smallest positive ...
February 16, 2016

Quick calc question
since lnx is defined only for x > 0 it's integral can be defined only for x>0 You figure out which of the choices matches that, I love and prefer the good ol' way of expressing relationships like that.
February 16, 2016

Quick calc question
∫1/x dx from 1 to 2 = lnx | from 1 to 2 = ln2 - ln1 = ln2 , since ln1 = 0
February 16, 2016

geometry please help!
#1 your function is a parabola #2. y=5-2/3x -- linear, if you mean 5 - (2/3)x y=5x^2+7 -- obviously non-linear y=1.5x-0.25 y=3 y=10/x+20 --- non-linear #3 y=3/4x-7/8 --> a straight line if you mean (3/4)x - 7/8 a curve if you mean 3/(4x) - 7/8
February 16, 2016

Math
c = √(76.4^2 + 39.3^2) = ...
February 16, 2016

maths
clearly you will have to cut some of the 4x8's If we place the long side of the 4x8 along the long side of the floor, we will need 3 sheets, with some cut off. We will then have the 4 ft part along the 13 ft part of the floor, needing 4 sheets with lots of waste. This &...
February 16, 2016

math
If the time is the same, and the rate is the same, the area of the two fields must be equal so (40)(w) = 20^2 w = 400/40 = 10 A farm which is 10 m wide ? mmmhhh....
February 16, 2016

MATH
If I understand the definitions correctly, "surface area" would be the total of all the areas of an object, while "lateral" surface area would exclude the base so the surface area of a square pyramid = area of the square base + 4(area of the triangle) That...
February 16, 2016

algebra
speed on first trip --- x km/h speed on return trip -- x+2 km/h recall that time = distance/rate difference in their times = 2 hrs ----> 240/x - 240/(x+20) = 2 everybody times x(x+20) 240(x+20) - 240x = 2x(x+20) 240x + 4800 - 240x = 2x^2 + 40x x^2 + 20x - 2400 = 0 (x-40)(x...
February 16, 2016

occupation
According to "Weigh-Watchers" tables, most herbs have no points.
February 16, 2016

math
correct
February 16, 2016

math
on the same grid, graph both y = x, which is a straight line, with slope 1 y = sinx http://www.wolframalpha.com/input/?i=plot+y+%3D+x,+y+%3D+sinx What do you notice? Where do they intersect ? slope of y = sinx = dy/dx = cosx when x = 0, cos0 = 1 for any value of -π/2 <...
February 15, 2016

Math
t = k/r, where k is a constant given: t = 5, r = 60 5 = k/60 k = 300 t = 300/r when r = 40 t = 300/40 = 7.5 hrs
February 15, 2016

math
Now: Jared --- x Eric ---- 2x 10 years ago: Jared --- x - 10 Eric -----2x-10 x-10 + 2x-10 = 19 solve for x
February 15, 2016

Math: Angles of Elevation and Depression
Once you make your sketch it is easy to see that tan40 = h/30 solve for h, the height of the pole
February 15, 2016

Math
so x+y=2 and xy=2 from the first: y = 2-x into the 2nd x(2-x) = 2 2x - x^2 - 2 = 0 x^2 - 2x + 2 = 0 solving by completing the square: x^2 - 2x = -2 x^2 - 2x + 1 = -2+1 (x-1)^2 = -i x-1 = ± √-1 = ± i x = 1 ± i
February 15, 2016

Math
x = (-√2 ± √(2 - 4(1)(1/2)) )/2 = - √2/2 ahh, then it must have factored sure enough (x + √2/2)^2 = 0 x = -√2/2 no need for complex numbers, the root is real.
February 15, 2016

math
your post is riddled with confusion is that log5 4 ?? what about the log5 -2x ? - is that log5 (-2x) ? and the log31, is that base 10 ? Normally when we don't state a base, it is understood to be 10
February 15, 2016

math
since he want to have 100,000 "forever" he will need a fund so that 6% of it = 100000 .06x = 100000 x = 1,666.666.67 so he has to accululate that much in 30 years, let the annual amount to save be P P(1.06^30 - 1)/.06 = 1,666,666.67 P = 21,081.15 is needed each year
February 15, 2016

math
what is 5700(1.0275)^12 ?
February 15, 2016

math
number of 25 rupees tickets ---x number of 30 rupees tickets --- 40-x 25x + 30(40-x) = 1125 solve for x #2 John ---x Babita -- 3x Ahmed ---5(3x) = 15x so ......
February 15, 2016

8th grade math - Variations
#1, good #2. yes #3. yes #4. yes in #3, and #4 aren't you supposed to write the equation? y = 3.5x , where x is in hours, and y is miles and d = 6.2t , where t is in hours and d in miles
February 15, 2016

Math
perfectly suitable for your question: http://davidmlane.com/hyperstat/z_table.html best on the web for stats
February 15, 2016

Math
show me your steps, it only takes 2 lines
February 15, 2016

Math
Just translate the English into Math "the length of the sides of each pen if the sides of the triangular pen are 16 less than twice a side of the square Pen." if side of square is x side of triangular pen is 2x-16 perimeter of square --- 4x perimeter of triangle -- 3...
February 15, 2016

Math
number of student tickets --- x number of guest tickets ----- 400-x solve for x 40x + 60(400-x) = 18500
February 15, 2016

Math College Algebra
No you can't use the formula for #1 If a = 0 , as it would be for the missing x^2 term, in the formula we are dividing by 2a and since we can't divide by zero, any results would be totally meaningless. So when "they" told you it could be done, tell "them...
February 15, 2016

Math College Algebra
re your question about the 13/12 in completing the square, the first thing you do is divide each term by the coefficient of the square term so you have x^2 in front - then take half of the middle term coefficient: 1/2 of 13/6 is 13/12 now square that and add to both sides (13/...
February 15, 2016

Math College Algebra
no, you can't do any of that. Since the 3 methods apply to quadratics and you don't have a quadratic in #1, the question is bogus. (That's like asking for 3 ways to bring a sailboat into a dock, when you sitting on a bicycle. )
February 15, 2016

Math College Algebra
first of all, the #1 is a linear function So the three methods you are asked to use apply to a quadratic function. So either silly or a typo. I will do the hard one, you must be able to do the other. -6x^2 - 13x + 5 = 0 6x^2 + 13x - 5 = 0 check if it factors: 6*(-5) = -30 does...
February 15, 2016

Calc 12
by the product rule ... f '(x) = (x^2 + 1)(-1)e^(-x) + 2x e^-x = e^-x (-x^2 - 1 + 2x) for a max or min, f '(x) = 0 e^-x (-x^2 - 1 + 2x) e^-x = 0 ---> not possible or x^2 -2x + 1 = 0 (x-1)^2 = x = 1 f(1) = (1+1)e^-1= 2/e = appr .736 check the ends since we are given ...
February 15, 2016

MATHS
If you mean: 9/(2x) = 10 - 8/x , then ... times 2x 9 = 20x - 16 20x = 25 x = 25/20 = 5/4
February 15, 2016

Math,algebra
Just check your answer with the "wording" of the question. First of all it asked for their present ages, so you would need two numbers. I assume you are saying, that the mother is 24, then the daughter is 4 Three years from now, Mother would be 27 and daughter would ...
February 15, 2016

Math,algebra
did it here: http://www.jiskha.com/display.cgi?id=1455540334
February 15, 2016

Math
number of P50 --- x number of P20 ----48-x their value: 50x + 20(48-x) = 1500 solve for x
February 15, 2016

Math
one number --- x the other ----- 2x+3 their sum = 3x+3 65 < 3x+3 < 75 subtract 3 62 < 3x < 72 divide by 3 62/3 < x < 24 but x is to be an integer, so the next integer after 62/3 is 21 21 ≤ x < 24 so the only numbers possible are 21, 22, and 23 as ...
February 15, 2016

Math
.08 on your 1.2 million will yield 96000 a year or $8000 per month you want to live on 80% of 64000 = 51200 or 4266.67 and you are getting 2500 per month from SC so all you need from you nest-egg is $1766.67 per month The problem is that you are not likely to get 8% these days.
February 14, 2016

Math
so you want to have 70000/12 or $5833.33 per month. Your social security gives you 2500 of that, so you need an extra $3,333.33 from your account
February 14, 2016

trigonometry
That circle equation would be x^2 + y^2 = 1 sub the y = -x into the circle x^2 + x^2 = 1 2x^2 = 1 x^2 = 1/2 x = ±1/√2 if x = +1/√2, y = -1/√2 finish it up
February 14, 2016

Calculus
remember that d(s)/dt = v(t) and acceleration = v ' (t) s(t) = (1/3)t^3 - (9/2)t^2 + 18t + c given s(0) = 1 1 = 0-0+0+c c = 1 s(t) = (1/3)t^3 - (9/2)t^2 + 18t + c s(0) = 1 s(8) = 512/3 - 288 + 144+1 = 83/3 avg velocity for first 8 seconds = (83/3 - 1)/(8-0) = 10/3 m/s v(5...
February 14, 2016

Math
amount = 3000(1.08^40 - 1)/.08 = ....
February 14, 2016

pre calculus
just did it
February 14, 2016

pre cal 11
S1 would be the first term S1 = 2+5 = 7 , so a = 7 S2 = 2(4) + 10 = 18 S2 = a + a+d = 18 14+d = 18 d = 4 the sequence is: 7, 11, 15, ... check: sum3 by formula = 2(9) + 15 = 33 by just adding the 3 terms = 7+11+15 = 33 All seems good
February 14, 2016

Math
Let the amount needed at the end of year year be P P(1.08^40 - 1)/.05 = 1.5 million P(259.0565187 P = 5790.24
February 14, 2016

Algebra ASAP
I thought this question looked familiar. Did it on Friday http://www.jiskha.com/display.cgi?id=1455295033
February 14, 2016

Math
prob (2 boys) = 2 (3/6)(1/5) = 1/5 I multiplied by 2 since it could be boy from grade7 x boy from grade 8 or boy from grade8 x boy from grade 7
February 14, 2016

mathematics
so (1/5)x = 25 solve for x
February 14, 2016

Geometry 1
When you sketch the diagrams for ship A and B, the first one has sides of 150 and 100 with a contained angle of 115°. Ship B's diagram has two sides 150 and 100 with a contained angle of 110° the side opposite the smaller angle would be the shorter side. So without...
February 14, 2016

algebra
a+8d = 52 a+11d = 70 subtract them 3d = 18 d = 6 back into the first: a + 48 = 52 a = 4 term20 = a+19d 4 + 19(6) = 118
February 14, 2016

Maths
if red is 1, blue has to be 5, can't happen if red is 3 blue has to be 3 So only one case prob (of stated event) = 1/4
February 14, 2016

Maths
A) prob(waiting once out of 3) = C(3,1)(.45)(.55^2) B) Prob(waiting twice of 3 days) = C(3,2) (.45^2)(.55) = ...
February 14, 2016

Calculus
intersection of y = x and y = 6-2x x = 6-2x 3x = 6 x = 2 , so y = 2 so you have a triangle with vertices (0,0), (2,2) and ((3,0), the last one is the x-intercept. Surely you don't Calculus to do this. base = 3, height = 2 Area = (1/2)(3)(2) = 3
February 14, 2016

Math
let their ages be 8x and 3x in 5 years: father's age = 8x+5 son's age is 3x+5 8x+5 + 3x+5 = 54 solve for x, plug into my definitions
February 14, 2016

Math
V = π r^2 h dV/dt = πr^2 dh/dt + 2πrh dr/dt pluggin in the given: dV/dt = π(10^2)(-.3) + 2π(10)(12).4 = ....
February 14, 2016

correction - Math
V = x^3 , where x is the length of the side dV/dt = 3x^2 dx/dt for the given data, dV/dt = 3(5^2)(9) = 675 cm^3/s S = 6x^2, where S is the surface area dS/dt = 12x dx/dt = 12(5)(9) = 540 cm^2/s
February 14, 2016

maths
x-------x-------x------ ... notice there are only two time intervals between the first and third strike so the time between strikes is 15 seconds Thus at 12:00 we would have 11 time intervals, and it would take 11(15) or 165 seconds
February 14, 2016

Maths
v = 17(cos105, sin105) = 17cos105 i - 17sin105 j since 105 = 60+45 degrees, and thus one of the "special" angles, they probably want exact values cos105 = cos(60+45) = cos60cos45 - sin60sin45 = (1/2)(√2/2) - (√3/2)(√2/2) = (√2 - √6)/4 ...
February 14, 2016

math
Just use a ratio weight/90 =20/120 weight = 90(20/120) = ...
February 13, 2016

Math
sum(8) = 4(2a + 7d) = 100 2a + 7d = 25 *** sum(20) = 10(2a + 19d) = 880 2a + 19d = 88 *** subtract them: 12d = 63 d = 21/4 in *** 2a + 7(21/4) = 25 2a = -47/4 a = -47/8 sum12 = 6(2(-47/8) + 11(21/4) = 276
February 13, 2016

Geometry
let the side of the triangle be 2x then tan60 = 8/x x = 8/tan60 perimeter = 3(2x) = 6x = 48/√3 = appr 27.7 cm
February 13, 2016

Geometry
tan32 = height/130 yes
February 13, 2016

Geometry
yes
February 13, 2016

Geometry
sin24° = height/3 height = 3sin24 = ...
February 13, 2016

algebra
Not going to follow the hint, why use 3 unknowns? I think the following way is easier: number of twenties -- x number of fives ------ x-1 number of ones = 34 - x - (x-1) = 35 - 2x 20x + 5(x-1) + 35-2x = 237 23x = 207 x = 9 So we have 9 twenties, 8 fives, and 17 ones check: ...
February 13, 2016

Math
8 1/3 % = 25/3 % = (25/3)/100 = 25/300 = 1/12 check: 1/12 = .083333 = 8.333...% =8 1/3 %
February 13, 2016

algebra
cost = 50 + .4x set 50 + .4x = 70 and solve for x
February 13, 2016

maths
sum(30) = sum(20) 15(2a + 29d) = 10(2a + 19d) divide by 5 and expand 6a + 87d = 4a + 38d 2a = -49d a = -49/2 sum(50) = 25( 2(-49/2)d + 49d) = 25(0) = 0
February 13, 2016

@ Steve - Trig
Steve , did not realize you had already given a detailed explanation. Patience would have indeed been a virtue that could have been exercised by the poster.
February 13, 2016

Trig
given : cscØ = √2 or by definition: sinØ = 1/√2 recall the CAST rule, which says that the sine is positive in quadrants I or II method 1: recognize the main trig ratios of 0°,30°, 60°, 45°, 90° we know that sin 45° = 1/√2...
February 13, 2016

DEAR REINY
Ok then, explanation accepted.
February 13, 2016

biostatics
using my favourite webpage for this topic ... http://davidmlane.com/hyperstat/z_table.html enter your mean and SD click on above and enter 72 to get .0912 so number of students = .0912(300) = appr 27
February 13, 2016

Math
like bobpursely said before Huh?
February 13, 2016

Math
started with x amount spent = (1/4)x + (1/8)x = (3/8)x leaving her with (5/8)x 5x/8 = 40 5x = 320 x = 64 Follow the same kind of reasoning for the 2nd question. Let me know what you did.
February 13, 2016

math
Four consecutive posts of unrelated questions with no work shown on your part. Looks like you want us to do your homework or your assignment for you. I did one of them for you, show me some work or effort on your part for the others, and I will help if you run into difficulties.
February 13, 2016

math
let the two parts be 5x and 3x "one part is 10 more than the other" ---> 5x = 3x+10 2x=10 x = 5 the two parts are 25 and 15, and the whole number was 40
February 13, 2016

maths( sets )
summary: F = 17 V = 15 R = 9 V only = 9 R only = 3 Then you ask "find the number of leaners who plays only volleyball and rugby." Wouldn't that be just 12 ???? What am I missing? btw, what is a leaner ? The question becomes interesting if you had asked to find ...
February 13, 2016

Calc 1
looks like a continuation of ... http://www.jiskha.com/display.cgi?id=1455252502 now you changed it to V^3-2v√v/v which clearly reduces to V^3-2√v and the derivative is even easier f(v) = v^3 - 2v^(1/2) f ' (v) = 3v^2 - v^(-1/2) or 3v^2 - 1/√v
February 12, 2016

Math
no 3 - 3x18 + 2 = 3 - 54 + 2 = -51 + 2 = -49 take your calculator and enter the calculations in the exact form 3 - 3x18 + 2
February 12, 2016

Pre-Calculus
complex roots come in conjugate pairs, so we know two roots to be -4i and 4i two factors would be (x-4i) and (x+4i) or (x^2 + 16) has to be a factor of f(x) so it would need another linear factor. since it ends in -48 and our x^2 factor end in +16, the remaining factor must ...
February 12, 2016

Finance
you will need a PV of 10700 x( 1 - 1.002^-96)/.002 = 10700 x(87.267434..) = 10700 x = 122.61 How did you get 147.65 ?
February 12, 2016

Math
3.75% compounded monthly: let the annual rate be i 1+i = (1 + .0375/12)^12 1+i = 1.038151.. i = .038151 = 3.8151 % follow the same steps I showed you in your previous post for the daily compounding question. Then compare the annual rates
February 12, 2016

MATH
All we need is the 4.75% per annum compounded daily Let the equivalent annual rate be i 1+i = (1 + .0475/365)^365 1+i = 1.0486429... So the annual rate is 4.864 %
February 12, 2016

geometry
I just see a right-angled triangle where sin55° = 21000/x x = 21000/sin55 = appr 25,636.3
February 12, 2016

MAth
You used simple interest on a compound interest problem. i = .0522/12 = .00435 n = 12(5) = 60 amount after 5 years = 5000(1.00435)^60 = 6487.47 interest earned = 1487.47
February 12, 2016

Math
(6x^-2)^2 (0.5x)^4 = (36/x^4)(1/16)(x^4) = 36/16 = 9/4
February 12, 2016

INTERMEDIATE ALGEBRA
quick way: the average of the three numbers would be 870/3 = 290 Since they are consecutive, they must be 289, 290, 291 long way: x + x+1 + x+2 = 870 solve for x, and state the numbers
February 12, 2016

Math
why do you think it is D ?
February 12, 2016

Math
if mean is 15.000 and we reject anything over 2 standard deviations away, we reject anything over 15.06 and under 14.94 go to http://davidmlane.com/hyperstat/z_table.html (the best stats page on the net) enter 15 for the mean enter .03 for SD click on between and enter 14.94 ...
February 12, 2016

Math
looks like a GP with a = 16, and r = 3/2 sum(7) = a( r^7 - 1)/(r-1) = 16(2187/128) - 1)/(1/2) = 32(2059/128) = 2059/4 or 514.75 how can the answer be 115.75 when the first 4 terms shown already add up to 130 ? Are you just guessing ?
February 12, 2016

Math
You must have meant: x = 2y^2 + 3y + 1 and 2x + 3y^2 = 0 so you are intersecting two parabolas both with a horizontal axis. I ran it through Wolfram, and it shows that they do not intersect. http://www.wolframalpha.com/input/?i=plot+x+%3D+2y%5E2+%2B+3y+%2B+1+and+2x+%2B+3y%5E2...
February 12, 2016

Trigonometry Help please
Both are done the same way, I will do the first, you do the second tanØ = 3/4 and Ø is acute, thus in the first quadrant sketch a right-angled triangle, with Ø at the origin , opposite side = 3 and adjacent side = 4 let the hypotenuse be r r^2 = 4^2 + 3^2...
February 12, 2016

math
(7.5 - 2cosØ)^2 = √(25 - 4sinØ)^2 (7.5 - 2cosØ)^2 = 25 - 4sinØ look at the left side it is always positive. The smallest value of 7.5 - 2cosØ is 4.5, when cosØ = 1 so the minimum value of the left side is 5.5^2 or 30.25 Now look ...
February 12, 2016

math
I see a skinny triangle with sides 10 and 12 with an angle of 165° between them If d is the distance between A and B d^2 = 10^2+12^2 - 2(10)(12)cos165 ... d = ... Once you have d, use the sine law to find the angle of the triangle at A sinA/12 = sin165/d ...
February 12, 2016

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