Percentages problem

[Mogorosi]

Concrete mixture A is composed of 35 percent cement, 40 percent sand, and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand, and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 75%

[beat_gmat_09]

Pick A - 100 units, B - 100 units.
35 units C from A 15 from B total - 50 units makes 25% of total (200)
A is 50% of Total (200)

[diebeatsthegmat]

Concrete mixture A is composed of 35 percent cement, 40 percent sand, and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand, and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 75%

A+B=25 percent cement
we can write the equation:
35A+15B=25(A+B)
so 10 A=10 B or A=B
so A/A+B=A/2A=1/2=0.5 or 50%
am i right?

[GMATGuruNY]

Concrete mixture A is composed of 35 percent cement, 40 percent sand, and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand, and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 75%

No complex math is needed here. Since the resulting percentage (25%) is halfway between the starting percentages (35% and 15%), we'll need equal amounts of A and B. Thus, 50% of the resulting mixture will be A.

The correct answer is D.