Working at their respective constant rates, machine A makes 100 copies in 20 minutes and machine B makes 150 copies in 10 minutes. If these machines work simultaneously at their respective rates for 30 minutes, what is the total number of copies that they will produce? Choices:
A) 250	B) 425	C) 675	D) 700	E) 600

Rationale: "machine a can produce 100 * 30 / 20 = 150 copies and , machine b can produce 150 * 30 / 10 = 450 copies total producing 600 copies . e is the answer"
Answer: E