Four typists can type a total of 600 memos in three days. At that rate, how many memos can three typists type in one day?
If four typists can type 600 memos in three days, they can type 200 memos in one day. Three typists can type $3/4$ of the memos in one day, or $200\cdot \frac{3}{4}=\boxed{150}$ memos.