If 20 typists can type 60 letters in 20 minutes, then how many letters will 30 typists working at the same rate complete in 1 hour?	Pick: A) 240 B) 200 C) 270 D) 300 E) 310

Rationale: "no . of letters typing by 20 typists in 20 minutes = 60 no . of letters typing by 20 typists in 60 minutes = 60 * 3 = 180 no . of letters typing by 30 typists in 60 minutes = 180 / 20 * 30 = 270 answer : c"
Answer: C