Stream of consciousness rationale: 25% of the apples are sour because 100 - 75 = 25. The average price of an apple sold is $.4 because .75(.5) + .25(.1) = .4. He got 100 apples because 40 / .4 = 100.
The question and answer pair are described below.
Q: Chang's Garden has two kinds of apples. Sweet ones and sour ones. He can sell the sweet ones for $.5 an apple. The sour ones sell for $.1 an apple. 75% of the apples he gets are sweet and the rest are sour. If he earns $40, how many apples did his trees give him?
A: 100