Machine A produces 100 parts twice as fast as Machine B does. Machine B produces 100 parts in 20 minutes. If each machine produces parts at a constant rate, how many parts does Machine A produce in 8 minutes? Choose the correct answer:
A) 100 B) 90 C) 80 D) 30 E) 50

Rationale: "machine b produces 100 part in 20 minutes . machine a produces 100 parts twice as fast as b , so machine a produces 100 parts in 20 / 2 = 10 minutes . now , machine a produces 100 parts in 10 minutes which is 100 / 10 = 10 parts / minute . 10 parts x a total of 8 minutes = 80 c"
Answer: C