Two mixtures of clay and sand contain 40% and 70% sand by weight. When both the mixtures are mixed, the resultant mixtur

[Gmat_mission]

Two mixtures of clay and sand contain 40% and 70% sand by weight. When both the mixtures are mixed, the resultant mixture is 700 gm. If the resultant mixture contains 45% clay by weight, then what is the weight of the first mixture?

A) 254.5 gm
B) 300 gm
C) 350 gm
D) 445.5 gm
E) 583.3 gm

Answer: C

Source: e-GMAT

[Scott@TargetTestPrep]

Two mixtures of clay and sand contain 40% and 70% sand by weight. When both the mixtures are mixed, the resultant mixture is 700 gm. If the resultant mixture contains 45% clay by weight, then what is the weight of the first mixture?

A) 254.5 gm
B) 300 gm
C) 350 gm
D) 445.5 gm
E) 583.3 gm

Answer: C

Solution:

If the first mixture contains 40% sand, then it contains 60% clay. Similarly, if the second mixture contains 70% sand, then it contains 30% clay. Since the resultant 700-gram mixture contains 45% clay and 45% is exactly the average of 60% and 30%, we must have an equal amount (in weight) of the first mixture and second mixture. Therefore, the weight of the first mixture is 700/2 = 350 grams.

Answer: C