# Posts by Reiny

Total # Posts: 38,653

**Math-Please Help**

nope, show your steps so I can see where you went wrong.

**Mathematics**

I always taught that 0/0 was indeterminate and did not fall into the "undefined" category. Such as in limits that result in 0/0 situations, e.g. lim (x^2 - 4)/(x-2) , as x ---> 2 you would get 0/0 = lim (x-2)(x+2)/(x-2) as x ---> 2 = limi x+2 , as x --->2 = ...

**Mathematics**

here is another explanation: if multiplication is repeated addition, e.g. 3x4 = 3+3+3+3 = 12 and division is repeated subtraction: e.g. 20 ÷ 4 20-4 = 16 16-4 = 12 12-4 = 8 8-4 = 4 4-4 = 0 I subtracted the 4 five times to get to zero so 20÷4 = 5 so how about 20 &...

**Mathematics**

Look at these cases: 12/3 = 4 because 3x4 = 12 20/10 = 2 because 2x10 = 20 5/0 = ?? because ?? x 0 = 5 , but that is a contradiction, since anything times zero is zero. or 5/.1 = 50 5/.01 = 500 5/.001 = 5000 5/.000000000001 = 5000000000000 notice I am dividing by a smaller and...

**science**

let the distance be x km time for first bus = x/54 time for 2nd bus = x/36 total time = x/54 + x/36 = 5x/108 total distance = 2x avg speed = total distance / total time = 2x / (5x/108) km/h = 108/5 km/h = 21.6 km/h

**Maths**

number of fivers --- x number of twos ---- 3x 5x + 2(3x) = 77 solve for x and state conclusion

**Math**

let the total be x students so x/3 + x/4 + x/6 + 18 = x multiply by 12 4x + 3x + 2x + 216 = 12x finish it up

**maths**

I would use substitution. from x-2y = 0 ---> x = 2y sub that into the 2nd: 3(2y)+ 4y = 20 continue to find y, then replace in x = 2y

**Math**

The algorithm I use sets it up this way: D = -3(3-0) - 2(0 - (-3)) - 3(0 - (-3)) = -9 -6 - 9 = -24 KhanAcademy shows 2 basic methods https://www.khanacademy.org/math/algebra-home/alg-matrices/alg-determinants-and-inverses-of-large-matrices/v/finding-the-determinant-of-a-3x3-...

**math**

(5/8) ÷ (y/9) = 9/8 5/8 = (9/8)(y/9) 5/8 = y/8 y = 5

**math**

yes

**math**

vertical asymptotes have slopes which are undefined. An answer of "undefined" is caused by division of zero. So what is your conclusion?

**Final Maths**

For half-life questions, it is usual to use a base of 1/2 or .5 amount = 12 (1/2)^(t/5700) , where t is the number of years if the amount = 10 10 = 12 (.5)^(t/5700) .8333... = .5^(t/5700) take logs of both sides and use log rules log .8333... = (t/5700) log .5 t/5700 = log ....

**Math - probability**

out of the 224, the expected number of A+ i = .357(224) = 79.968 or 80 cases out of the 224, the expected number of AB- = .006(224) = .... carry on

**Math**

2. multiply the probability you found in 1. by 60

**Calculus - Fundamental thm of Calc**

To fully understand what Steve did, watch these two KhanAcademy clips https://www.khanacademy.org/math/ap-calculus-ab/fundamental-theorem-of-calculus-ab/fundamental-theorem-of-calculus-tut-ab/v/fundamental-theorem-of-calculus and https://www.khanacademy.org/math/ap-calculus-ab...

**Math**

let the angles in the interior of the triangle be x, y, and z Extend the base at the z angle let the exterior angle be k we know x+y+z = 180° we know that the z + k = 180 , (angles forming a straight line) so x+y+z = z + k x + y = k state your conclusion

**fgh**

Not being familiar with the game of cricket, I find this sentence confusing: "A team of 11 players must have at least 5 batmen, 4 bowlers and 1 wicket-keeper" Assuming that you would want 11 players, that could mean: 6 batmen, 4 bowlers, 1 wicket-keeper; 5 batmen, 5 ...

**math**

Really? How can you claim that it is negative, after having it shown that it is positive. Look at the calculation.

**math**

first one: slope = (5-1)/(6-3) = 4/3 how did you get it to be negative? 2nd: slope = (-5-(-6))/(-3-(-3)) = 1/0 can't divide by zero, so "undefined"

**Algebra**

t(1) = 3 = 1x3 t(2) = 8 = 2x4 t(3) = 15 = 3x5 t(4) = 24 = 4x6 t(5) = 35 = 5x7 .. looks like t(n) = n x (n+2) so t(11) = 11x13 = 143

**Pre calculus**

term(1) = 1^2 -2 = -1 term(2) = 2^2 - 2 = 2 term(3) = 3^2 - 2 = 7 term(4) = 4^2 - 2 = 14 ... term(n) = n^2 - 2 62 = 8^2 - 2 , so we have 8 terms sigma (n^2 - 2) for 1 to n = n(n+1)(2n+1)/6 - 2n recalling that sum n^2 = n(n+1)(2n+1)/6 checking for sum(5) = 5(6)(11)/6 - 10 = 55-...

**Probability**

odds are defined slightly different from probability. odds in favour of some event = prob(of that event) : prob (not that event) so odds in favour of rain on Sept 21 = .358 : .642 = 358 : 642 reduce to lowest term ratio

**Math (ugh)**

Don't know what the hangup is between mixed fractions and "improper" fractions mixed fractions may be nice to look at, but they are basically useless for arithmetic calculations and must be changed to improper fractions so, 3 3/4 x 2 4/5 = (15/4)(14/5) = (3/2)(7/...

**Math 1**

80x^4 - 60x^3 - 60x^2 - 45x This one looks more promising. = 5x(16x^3 - 12x^2 - 12x - 9) let f(x) = 16x^3 - 12x^2 - 12x - 9 f(±1) ? 0 f(±3) ? 0 tried ±3/2, ±3/4, ±3/8, ±3/16 found f(3/2) = 16(27/8) - 12(9/4) - 12(3/2) - 9 = 54 - 27 - ...

**Math1**

Well, let's look at everything again. clearly x^2 is a common factor. Look at the numbers, start with the 24 24 = 3*8 = 3*2*2*2 so the 195 is only divisible by 3 but not 28, so the HCF is x^2 195x^5 + 168x^4 - 28x^3 - 24x^2 = x^2(195x^3 + 168x^2 - 28x - 24)

**Math**

review your rules of exponents as it applies to division of powers. This one is a straightforward application of one of those rules. If this is for a test, you MUST know this. btw, x^9/x^2 is the same as x^9 ÷ x^2

**algebra**

did you mean log(2x-6)^256=4 ?? according to the numbers, I will assume so. You must know your rules of logs by definition 256 log (2x-6) = 4 log (2x-6) = 1/64 2x-6 = 10^(1/64) 2x-6 = 1.0366329.. 2x = 7.0366... x = 3.518316... round to whatever accuracy you want. that answer ...

**Statistics**

I only answered part b) since a) is very simple a) would be .51^7 = .0089741 I have no idea how yo got 8.9741, the digits are the same, but no probability can be greater than 1. for b) the answer correct to 4 decimals is .0494, your is correct only to 3 decimals

**Statistics**

prob(b) = .51 prob(x) = .49 , where x is "not blue eyes" one such case could be xxbxxxx , which would be (.51)(.49^6) but there are 7 such cases, so prob(your event) = 7(.51)(.49^6) = .... in stats notation: C(7,1)(.51)(.49)^6

**maths**

R = k/r^2 when R = .24, r = .05 .24 = k/.0025 k = .006 when r = .04 R = .006(1/.0016) = .375

**calculus**

done, look back

**clculus**

dy/dx = 2x at (-2,4), slope = -4 equation of tangent: y-4 = -4(x+2) y = -4x -4 let x = t y = -4t - 4

**Maths**

Assuming you mean: 4x^2 - 5x - 1 = 0 x = (5 ± ?41)/8 so alpha = (5+?41)/8 and beta = (5-?41)/8 a^2b = (5+?41)/8 * (5+?41)/8 * (5-?41)/8 = (5+?41)/8 * (25 - 41)/64 = (5+?41)/8 * (-16/64) = (-5-?41)/32 GAURAV concluded that a = 1, b = 1/4 but those are not the zeros of ...

**Math**

What is 6x15 ?

**MAth**

Of course the bisector of angle C is 45° let the bisector hit AB at P in triangle BCP tan 45 = BP/15 BP = 15tan45 = 15 continue

**alg II**

yes, and yes

**Calculus**

yes

**geometry please help!!!!**

I made a rough sketch. For the total surface area I see two equal trapezoids, and 4 rectangles. the rectangles are: 14 by 10 , 8 by 10 and 2 of 5 by 10 the area of the trapezoid = (1/2)(8+14)/2 finish the arithmetic and use the correct units

**math help please check my answer**

tan Ø = 60/25 = 2.4 Ø = tan^-1 (2.4) = 67.38..° = 67° to the nearest degree

**math**

I disagree, Odds and probability are defined slightly different. The odds of some event happening = prob( event) : prob(not the event) so if prob(a 21 ) = 1/38 then the prob(not a 21 ) = 1 - 1/38 = 37/38 odds in favour of a 21 = (1/38) / (37/38) = (1/38)(38/37) = 1 : 37

**Pre calc**

Or for the 2nd Cos 2x cosx -sin 2xsinx = 0 Cos(2x + x) = 0 cos 3x = 0 3x = pi/2 or 3x = 3pi/2 x = pi/6 or x = pi/2 The period of cos 3x = 2pi/3 So add multiples of that together Steve's other answers

**math**

the sixth term of an arithmetic progression is 37 ---> a+5d = 37 5d = 37-a sum of the first six term is 147 ---> (6/2)(2a + 5d) = 147 3(2a + 37-a) = 147 a +37 = 49 a = 12 d = 5 If you had a question, take it from there

**Math**

Juan's present age --- x Ben's present age ---- x+4 in two years: Juan ----- x+2 Ben -------x=4+2 = x+6 x+2 + x+6 = 50 continue

**MAth**

2l + 2w = 240 l + w = 120 l = 120-w new length = 1.1l new width = .8w 2(1.1l) + 2(.8w) = 240 1.1l + .8w= 120 1.1(120-w) + .8w = 120 11(120-w) + 8w = 1200 1320 - 11w + 8w = 1200 -3w = -120 w = 40 then l = 120-40 =80 state a proper conclusion

**Mathmatics**

slope of line Q = (-8+2)/(-8+10) = -6/2 = -3 slope of line R = (a-2)/(10-1) = (a-2)/9 but they are perpendicular, so (a-2)/9 = -1/3 continue

**Mathmatics**

let B be (x,y) for the x: (x-3)/(12-x) = 2/1 x - 3 = 24 - 2x 3x = 27 x = 9 find the y in the same way

**Mathmatics**

slope AB = m = (1+7)/(-8+12) = 8/4 = 2 using (2,5) y-5 = 2(x-2)

**Maths**

sub in the two points to set up two equations for (0,3) 3 = a b^0, but b^0 = 1 so a = 3 for (2,12) 12 = 3 b^2 4 = b^2 b = ± 2, but we need b> 0 a = 3 , b = 2 ---> y = 3 (2)^x

**math**

dc/dq=0.08q^2-1.8q+2.5 c = (.08/3) q^3 - .9 q^2 + 2.5q + 5000 plug in 1000 for q

**math**

I would expand it first, y = 4x^-2 + x^-5 now it is elementary.

**Mathematics**

Surface area of original = 2(11)(6) + 2(11)(4) + 2(6)(4) cm^2 = 268 cm^2 volume of original = (11)(6)(4) cm^3 = 264 cm^3 For a cube to hold 264 cm^3, each side must be 264^(1/3) or 6.415... cm long surface area of the cube = 6(6.415...)^2 = appr 246.92 cm^2 (I only rounded ...

**QMI**

amount = 2000(1.1^35 - 1)/.1 = ....

**precalculus**

p = 32 e^(kt) , where k is a constant when t = 3, p = 200 32 e^(3k) = 200 e^(3k) = 6.25 3k = ln 6.25 k = appr .61086 p = 32 e^(.61086 t)

**Trig**

Fish at a depth of 45 km in Lake Ontario ???? I live about 45 minutes from Lake Ontario, and let me guarantee you that lake is not that deep, lol. Anyway ..... I will assume you meant 45 m. let the line be l m long cos 45 = 46/l ----- ( 1 m above the water + 45 l = 46 m) l = ...

**precalculus**

If I read it correctly you want 230000(.95)^t = 150000(1.11)^t 23(.95^t) = 15(1.11)^t take logs of both sides and use log rules log 23 + t log .95 = log 15 + t log 1.11 log 23 - log 15 = t(log 1.11 - log .95) carry on

**math**

What are you trying to do ?? is it 6 = e^(5r) or the way you typed it?

**math**

correct, but remember that q will be half-years so you will have to divide q by 2 to get the number of years

**College Algebra**

good grief! I just did this for you a few minutes ago!!!!

**Help College Algebra**

At what will the ball be ... ????? Time ?? set -16t^(2)+128t = 213 and solve 16t^2 - 128t + 213 = 0 you will get two answers, one positive and one negative. Reject the negative answer.

**College Algebra**

Besides that , it was already answered.

**College Algebra**

V = (1/3)? r^2 , solve for r 3V/? = r^2 r = ±?(3V/r)

**algebra**

a) x = 5y ? 3 5y = x+3 y = (1/5)x + 3/5 b) the slope is 1/5, they are the same equation c) they are the same equation

**Algebra**

d=kt^2 kt^2 = d t^2 = d/k t = ± ?(d/k)

**Algebra**

part one, height = 32 -16t^2 + 32t = 32 t^2 - t +1 = 0 by the formula: t = (1 ± ?-3)/2 , not real so it will never reach a height of 32 ft we can see that by noting that the x-intercepts are 0 and 2 so the vertex is at t = 1 max height is h(1) = -16+32 = 16 I also ...

**metric unit**

behold the beauty of the metric system 48567 kg = 48.567 tons

**Math**

clearly B

**Math**

No, this is an example of Binomial Distribution. You are planting 7 plants, and you want the prob that exactly 1 does not grow. Suppose it is the 3rd plant which did not grow. GGNGGGG, where G stands for grow, N for not grow. That specific probability is (.7)(.7)(.3)(.7)(.7)(....

**Math**

same question here: http://www.jiskha.com/display.cgi?id=1445605410

**francis**

the 8th term of an A.P is twice the 5th term ----> a + 7d = 2(a+4d) a+7d = 2a + 8d a = -d 12th term = a + 11d = -d + 11d = 10d e.g. let d = 4, then a = -4 term(8) = -4 + 7(4) = 24 term(5) = -4 + 4(4) = 12 so term 8 is twice term 5 term 12 = -4+11(4) = 40 which is 10d or 10(...

**Math**

I would just use a simple ratio. 29/35 : 6/35 = 29 : 6 since 3 5/12 = 41/12 so x/(41/12) = 6/29 29x = 6(41/12) = 41/2 x = 41/58 quarts needed to finish the job

**Maths**

surface area = 2 circles + 1 rectangle = 2?r^2 + (2?r)(h) = 2?(5^2) + 2?(5)(15) = 50? + 150? = 200? cm^2 1 m^2 = 10000 cm^2 so our surface area = 200?/10000 m^2 cost = 4500(200?/10000) naira = 90? naira = ..... I will let you do the arithmetic

**Maths**

rest of distance = 1 - (3/8 + 3/5) = 1 - 39/40 = 1/40 (1/40)x = 2 x = 80 km so he went (3/5)(80) km by bus = .....

**Maths**

volume = length x width x height = (85)(62)(36) cm^3 = .. continue

**maths**

done here http://www.jiskha.com/display.cgi?id=1492480948

**arithmatic series**

quotient of the larger number and the smaller number is just a list of the terms e.g. a,b,c,d,.. the series is the sum of those arithmetic terms a+b+c+d+..

**math**

larger --- L smaller --- 74-L "quotient of the larger number and the smaller number" ---> L/(74 - L)

**math**

done here http://www.jiskha.com/display.cgi?id=1492424429

**math**

15, 15+d, 15+2d, 15+3d, 15+4d, 87 87 - (15+4d) = d 72 - 4d = d 5d = 72 d = 72/5 = 14.4 15, 29.4, 43.8, 58.2, 72.6, 87

**math**

a = -13 , d = 5 term(n) = a + (n-1)d = -13 + 5(n-1) = -13 + 5n - 5 = 5n - 18

**maths**

you have an AS sum = 4000 + 5000 + 6000 + .. sum(n) = (n/2)(8000 + (n-1)(1000) ) = 60000 n(8000 + 1000n - 1000) = 120000 1000n(7 + n) = 120000 n(n+7) = 120 n^2 + 7n - 120 = 0 (n - 8)(n + 15) = 0 n = 8 or n = -15, ignore the negative They can be late 8 days

**correction - Calculus**

I jumped to conclusion when I subbed in the 0 (4/(1/3) (x+1)^(1/3) from 0 to x = 12(x+1)^1/3 from 0 to x should have given me: 12 (x+1)^(1/3) - 12(1)^(1/3) = 12 (x+1)^(1/3) - 12 f(x) = 12 (x+1)^(1/3) - 12 f(26) = 12(3) - 12 = 24

**Calculus**

so you want f(x)= ? 4 (x+1)^(-2/3) dx from 0 to x = (4/(1/3) (x+1)^(1/3) from 0 to x = 12(x+1)^1/3 so f(26) = 12(27)^(1/3) = 12(3) = 36

**math**

a metre and a centimetre are units of length if I told you that a nickel has a mass of about 5 grams, and a quart of milk has a mass of about 1 kg, what is your conclusion ?

**Math**

children --- x adults ------2x Joe + wife + 4 children = 56 2x + 2x + 4x = 56 x = 7 state your conclusion.

**math**

in y = mx + b, the rate of change or slope is m consider y = 3 as y = 0x + 3 so the rate of change is zero, or "y does not change", it is always 3

**Math**

1000 words per 5 minutes = 1000/5 words per 1 minute or simply 200 words/min (you had 5/1000 which is not 200, but 1/200)

**Math**

or, using algebra let the two amounts invested by 6x and 7x (notice 6x : 7x = 6 : 7 ) then 6x + 7x = 260 13x = 260 x = 20 then 6x = 6(20) = 120 and 7x = 7(20) = 140 the same answers obtained by Ms Sue

**Statistics**

I will assume that you are working from "tables", so we need the z-score for 1550 z-score = (1550 - 1500)/200 = .25 look at http://math.arizona.edu/~rsims/ma464/standardnormaltable.pdf and find .25 (2nd page , find .2 in 1st column, then under .05) to find .59871 ...

**Statistics**

P(-2>Z and Z<-1) or more commonly written as P(-2 > Z <-1) wants you to find the probability that the z-score of the normal binomial distribution lies between -2 and -1 X~N(3,4) or X~N(3,2^2) means X is normally distributed with a mean of 3 and a standard deviation...

**Math**

in d = 25h the distance travelled "depends" on the time taken, so ......

**Math**

for a mean of 541, with a sd of 89 we would have: 541-89 <---> 541+89 (one standard deviation) 452 <---> 630 ---------68% 452-89 <---> 630+89 (two standard deviations) 363 <---> 719 -------- 95% since 541 is the mean 363<---> 541 would be 1/2 of ...

**Steve to the rescue**

Of course, why didn't I think of that 2 data values --- linear 3 data values --- quadratic 4 data values --- cubic etc

**series maths steve reiny bob reiny steve!!!**

Looking at only 3 terms, they are not in AP they are not in GP looking for some pattern: 8 = 4*2 20 = 4*5 52 = 4*13 I see nothing special about 2, 5, 13 2 = 1+1 5 = 4+1 13 = 12+1 still nothing

**math**

meant to say at the end: I get 2 pairs of solution for a and d, one will work, the other causes a 0 to show up in a GP, which is not possible.

**math**

let the four number be a, a+d, a+2d , a+3d then given: a+5, a+d+6, a+2d+9, a+3d+15 are in GP then (a+d+6)^2 = (a+5)(a+2d+9) a^2 + d^2 + 36 + 2ad + 12a + 12d = a^2 + 2ad + 9a + 5a + 10d + 45 d^2 - 2a + 2d = 9 a = (d^2 + 2d - 9)/2 (a+2d+9)^2 = (a+d+6)(a+3d+15) I get: - 3a + d^2...

**financial mathematics**

perhaps "alternative facts" are even entering the world of math, lol, strange times

**financial mathematics**

i = .16/4 = .04 n = 5(4) = 20 PV = payment (1 - (1+i)^-n)/i P( 1 - 1.04^-20)/.04 = 1000 P = .04(1000)/(1 - 1.04^-20) = 73.58

**maths**

After you make your sketch and draw the parallogram, I would use the cosine law: |R|^2 = 16^2 + 16^2 - 2(16)(16)cos 120° = 512 - 256(-1/2) = 640 |R| = ?640 = appr 25.3

**Pre calc**

tanØ = 2?10/9 recall tanØ = y/x in the corresponding right-angled triangle we are also given that cscØ is negative, so Ø must be in III then y = -2?10 and x = -9 r^2 = 40 + 81 =121 r = 11 x = -9, y = -2?10, r = 11 sinØ = -2?10/11, cosØ...