If 20 typists can type 42 letters in 20 minutes, then how many letters will 30 typists working at the same rate complete in 1 hour? Choose the correct choice from the following options
A) 189
B) 72
C) 144
D) 216
E) 400
20 typists can type 42 letters, so 30 typists can type = 42*30/20   42*30/20 letters can be typed in 20 mins. In 60 mins typist can type= 42*30*60/20*20= 189   189 is the answer
<result>A</result>
If 20 typists can type 42 letters in 20 minutes, then how many letters will 30 typists working at the same rate complete in 1 hour?