1988 AJHSME Problem 23

Maria buys computer disks at a price of 4 for <dollar>5 and sells them at a price of 3 for <dollar>\$5. How many computer disks must she sell in order to make a profit of 100$?

\text{(A)}\ 100 \qquad \text{(B)}\ 120 \qquad \text{(C)}\ 200 \qquad \text{(D)}\ 240 \qquad \text{(E)}\ 1200

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.