crack Math question( I hate QR)

[far123]

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hey guys, I have two questions please:
1)In how many ways can 10 candidates be selected for 3 vacansies(5 male and 5 female) of which one vacancy is reserved for a female?
the anser is 41 but I think it should be 180... any body knows the right answer?
2) A sum of money is lent out at simple intrest which amount to 250$ in 2 years, and 300 $ in 3 years. what is the rate of intrest?
the answer is 100/3 and I have no idea how they calculate that. ( the explanation on crack MAth is toooo poor)

 

[TheGreenWave]

hey guys, I have two questions please:
1)In how many ways can 10 candidates be selected for 3 vacansies(5 male and 5 female) of which one vacancy is reserved for a female?
the anser is 41 but I think it should be 180... any body knows the right answer?
2) A sum of money is lent out at simple intrest which amount to 250$ in 2 years, and 300 $ in 3 years. what is the rate of intrest?
the answer is 100/3 and I have no idea how they calculate that. ( the explanation on crack MAth is toooo poor)

You are correct for the first one. Whoever wrote the question got 36 different possibilities by doing 9 C 2, since one is reserved for the female. since their are 5 different females they should have multiplied by 5 and got 180, but they messed up and added the five and got 41.

The second question is worded poorly. The formula is Amount accured from interest = IRT. investment*rate*time.

 

[dnascramble]

hey guys, I have two questions please:
1)In how many ways can 10 candidates be selected for 3 vacansies(5 male and 5 female) of which one vacancy is reserved for a female?
the anser is 41 but I think it should be 180... any body knows the right answer?
2) A sum of money is lent out at simple intrest which amount to 250$ in 2 years, and 300 $ in 3 years. what is the rate of intrest?
the answer is 100/3 and I have no idea how they calculate that. ( the explanation on crack MAth is toooo poor)

1)
9!/[2!(9!-2!)]= 9!/(2!*7!) = 9*8/2 = 36 and since there one vacancy is reserved for a female, add 5. so 36+5 = 41
(9! is used because one sit is reserved)

 

[PooyaH]

1)
9!/[2!(9!-2!)]= 9!/(2!*7!) = 9*8/2 = 36 and since there one vacancy is reserved for a female, add 5. so 36+5 = 41
(9! is used because one sit is reserved)

You are wrong my friend. Since it's saying there must be one vacancy reserved for a female; basically, there can't be all 3 males!!! So first get all the possibilities and subtract the number of possible ways for 3 men from the total number of possibilities!

 

[PooyaH]

hey guys, I have two questions please:
1)In how many ways can 10 candidates be selected for 3 vacansies(5 male and 5 female) of which one vacancy is reserved for a female?
the anser is 41 but I think it should be 180... any body knows the right answer?
2) A sum of money is lent out at simple intrest which amount to 250$ in 2 years, and 300 $ in 3 years. what is the rate of intrest?
the answer is 100/3 and I have no idea how they calculate that. ( the explanation on crack MAth is toooo poor)

Second Question:

I'm assuming that $250 and $300 are the amounts that are needed to be paid and not just the interest! So we use this simple interest formula:
A = P(1+rt) thus:

$250 = P [1 + r(2)] => P = $250 /(1 + 2r)

$300 = P [1 + r(3)] => P = $300 / (1 + 3r)

So:

$250 / (1 + 2r) = $300 / (1 + 3r)
250 + 750r = 300 + 600r
150r = 50
r = 50 / 150
r = 1/3 x 100 = 100/3

 

[td4azklz]

Second Question:

I'm assuming that $250 and $300 are the amounts that are needed to be paid and not just the interest! So we use this simple interest formula: I = P(1+rt) thus:

$250 = P [1 + r(2)] => P = $250 /(1 + 2r)

$300 = P [1 + r(3)] => P = $300 / (1 + 3r)

So:

$250 / (1 + 2r) = $300 / (1 + 3r)
250 + 750r = 300 + 600r
150r = 50
r = 50 / 150
r = 1/3 x 100 = 100/3

Yep, that's what i got too. Pooyah, I think you meant to say that this is a compound interest problem.

 

[PooyaH]

Yep, that's what i got too. Pooyah, I think you meant to say that this is a compound interest problem.

No this question is simple interest!

Simple interest formulas are:

I = Prt & A = P(1 + rt)

Compound interest formulas are:

I = P [(1 + r)^n -1] & A = P (1+r/n)^nt

 

[far123]

No this question is simple interest!

Simple interest formulas are:

I = Prt & A = P(1 + rt)

Compound interest formulas are:

I = P [(1 + r)^n -1] & A = P (1+r/n)^rt

thnx Pooya, these two formullas made my life way easyer

 

[far123]

No this question is simple interest!

Simple interest formulas are:

I = Prt & A = P(1 + rt)

Compound interest formulas are:

I = P [(1 + r)^n -1] & A = P (1+r/n)^rt

what is n though?

 

[PooyaH]

what is n though?

n is the number of times the interest is compounded per year

 

[Streetwolf]

You're all wrong on #1. The answer is 110.

This was posted a week ago and I'm heading out now so either accept the answer, search for it, or figure out how I did it. 🙂

Edit: PooyaH gave the correct method up there.

 

[PooyaH]

thnx Pooya, these two formullas made my life way easyer

btw, in my first post where I wrote the formulas I had A = P (1+r/n)^rt but it should be A = P (1 + r/n)^nt

I edited that though...sorry 😀

 

[far123]

n is the number of times the interest is compounded per year

thnx

 

[TheGreenWave]

You're all wrong on #1. The answer is 110.

This was posted a week ago and I'm heading out now so either accept the answer, search for it, or figure out how I did it. 🙂

Edit: PooyaH gave the correct method up there.

I dont think anyone on this forum has the balls to second guess you in math. im pissed i missed it. oh well for everyone else, i did the search and of course streetwolf is right here is his previous explanation:

This was in another thread a while back. The answer key is wrong. The answer should be 110.

The best way to do this, and also the easiest to understand, is to start with the total number of 3 person groups. This is just (10 C 3) = 120. Now the question says one spot is reserved for a woman. This is a fancy way of saying that at least one woman is in the group. So to do that, you take all the possible cases and subtract the number of cases that have only men. Then you're left with all the cases with at least 1 woman.

All men = (5 C 3) * (5 C 0) <-- choose 3 men out of 5, choose 0 women out of 5

This equals 10.

So 120 - 10 = 110, your answer.
__________________
Stony Brook School of Dental Medicine
Class of 2011

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PS what did you get on QR streetwolf a 35?? i mean geez

 

[Streetwolf]

28.

And I made a mistake on SDN once I think 😛

 

[TheGreenWave]

28.

And I made a mistake on SDN once I think 😛

WOW!!!!!!!!! the dental schools must have thought you were taking performance enhancing supplements. i mean your QR score is clearly on steroids.