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# If a certain concrete mixture contains gravel, water, and sand in a 1

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VP
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If a certain concrete mixture contains gravel, water, and sand in a 1  [#permalink]

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14 Sep 2018, 11:29
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Difficulty:

15% (low)

Question Stats:

84% (00:33) correct 16% (00:46) wrong based on 32 sessions

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If a certain concrete mixture contains gravel, water, and sand in a 1 to 3 to 5 ratio by weight, how many pounds of gravel would be needed to produce 72 pounds of the mixture?

1. 72

2. 40

3. 24

4. 9

5. 8

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Joined: 02 Sep 2015
Posts: 42
Re: If a certain concrete mixture contains gravel, water, and sand in a 1  [#permalink]

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14 Sep 2018, 11:35
1
$$1X + 3X + 5X = 72$$
$$9X = 72$$
$$= 8$$

GMATH Teacher
Status: GMATH founder
Joined: 12 Oct 2010
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Re: If a certain concrete mixture contains gravel, water, and sand in a 1  [#permalink]

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19 Sep 2018, 19:39
AkshdeepS wrote:
If a certain concrete mixture contains gravel, water, and sand in a 1 to 3 to 5 ratio by weight, how many pounds of gravel would be needed to produce 72 pounds of the mixture?

1. 72

2. 40

3. 24

4. 9

5. 8

Trivial application of the k technique:

$$G:W:S = 1:3:5\,\,\,\,\, \Rightarrow \,\,\,\,\left\{ \matrix{ ? = G = k \hfill \cr W = 3k \hfill \cr S = 5k \hfill \cr} \right.\,\,\,\,\,\,\left( {k > 0} \right)$$

$$72 = 9k\,\,\,\, \Rightarrow \,\,\,\,? = k = {{72} \over 9} = 8\,\,\,\,\,\left[ {{\rm{pounds}}} \right]$$

This solution follows the notations and rationale taught in the GMATH method.

Regards,
fskilnik.
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Re: If a certain concrete mixture contains gravel, water, and sand in a 1 &nbs [#permalink] 19 Sep 2018, 19:39
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