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A boy is buying two kinds of marbles. One kind costs 25 cents per poun

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A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 03 Feb 2017, 07:08
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Question Stats:

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A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. If the boy spent approximately 29 cents per pound for everything, how many pounds of the more expensive marbles did he buy?

A. 5
B. 6
C. 7
D. 8
E. 9

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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 03 Feb 2017, 22:14
Suppose the boy bought x pounds of the expensive marbles.
so, we can say:
29(5+x) = 25*5 + x*32
=> 3x = 20
=>x = 6.67 ≈ 7.

Answer C.
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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 22 May 2018, 17:08
Bunuel wrote:
A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. If the boy spent approximately 29 cents per pound for everything, how many pounds of the more expensive marbles did he buy?

A. 5
B. 6
C. 7
D. 8
E. 9


We can let n = the number of pounds of the more expensive marbles that he bought and create the equation:

(25 x 5 + 32 x n)/(n + 5) = 29

125 + 32n = 29n + 145

3n = 20

n = 20/3 = 6 2/3 ≈ 7

Answer: C
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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 22 May 2018, 21:22
A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. If the boy spent approximately 29 cents per pound for everything, how many pounds of the more expensive marbles did he buy?

25 cents/pound = 5 pounds = 125 cents

29 (5+N) = 125 + 32N
145 + 29N = 125 + 32N
145+29N-125-32N
20-3N=0
3N=20

N ≈ 7

Ans: C
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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 23 Jun 2018, 07:31
Bunuel wrote:
A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. If the boy spent approximately 29 cents per pound for everything, how many pounds of the more expensive marbles did he buy?

A. 5
B. 6
C. 7
D. 8
E. 9


let the weight of more expensive marbles be x pounds

using weighted average method

weight of less expensive marbles = w1 = 5 lbs
weight of expensive marbles = w2 = x
rate of less expensive marble = 25
rate of more expensive marble = 32

rate of mixture of marbles = 29

w1/w2 = (32-29)/(29-25)

5/x = (32-29)/(29-25)
5/x = 3/4
x = 20/3 = 6.66 ~ 7
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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 23 Jun 2018, 07:43
Bunuel wrote:
A boy is buying two kinds of marbles. One kind costs 25 cents per pound and he purchased 5 pounds of this kind. The other kind of marble costs 32 cents per pound. If the boy spent approximately 29 cents per pound for everything, how many pounds of the more expensive marbles did he buy?

A. 5
B. 6
C. 7
D. 8
E. 9


The 25c marbles are 4c each below the average. Five were bought, so together that is 30c below average.

The 32c marbles are each 3c above average.

20c/3c is roughly equal to 7.

Answer is C.

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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 08 Oct 2018, 04:23
Bunuel PeepalTree ScottTargetTestPrep

Can you please explain in what all cases do we have to round up the approximations and in what all do we have to round down? I rounded down the 6.7 approximation to 6 and got wrong.
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A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 17 Oct 2018, 16:50
Hi Bunuel, having a great day, I hope. I have the exact question as BigUD94 has. Are we rounding up because the tenth place digit is greater than 5? Your explanation will be much appreciated. Thanks.

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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun  [#permalink]

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New post 18 Oct 2018, 06:44
BigUD94 wrote:
Bunuel PeepalTree ScottTargetTestPrep

Can you please explain in what all cases do we have to round up the approximations and in what all do we have to round down? I rounded down the 6.7 approximation to 6 and got wrong.

Kem12 wrote:
Hi Bunuel, having a great day, I hope. I have the exact question as BigUD94 has. Are we rounding up because the tenth place digit is greater than 5? Your explanation will be much appreciated. Thanks.

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Hi there!
Rounding up and Down is pretty easy. Just practice few questions with focus you will get it.

Check out these resources by Bunuel and veritasPrep
Rounding

Rounding up some OG question

Cheers!
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Re: A boy is buying two kinds of marbles. One kind costs 25 cents per poun &nbs [#permalink] 18 Oct 2018, 06:44
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