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

Question

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

magbot · Answer

1X + 3X + 5X = 72 
 9X = 72 
 = 8

Answer: E

fskilnik · Answer

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

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

Regards,
fskilnik.

ScottTargetTestPrep · Answer

We can create the ratio:

Gravel : water : sand = x : 3x : 5x

We can create the equation:

x + 3x + 5x = 72

9x = 72

x = 8

So the number of pounds of gravel is 8.

Answer: E

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