SAT Math

Answer: B - The workers need nine days to finish a job. After three, days two workers came, and the number of workers becomes (6 + 2). If the number of workers stayed the same (6), they will finish a job in (15 − 3) days. The numbers of workers and days vary inversely.

6:(6 + 2) = x:(15 − 3)
6:8 = x:12
8x = 6 × 12
x = (6 × 12)/8 = 9