Multiple choice general knowledge math & puzzles

A and B can do a piece of work in 45 days and 40 days respectively. They began to do the work together but A leaves after some days and then B completed the remaining work n 23 days. The number of days after which A left the work was

  1. 9

  2. 11

  3. 12

  4. 15

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let total work be 360 units (LCM of 45 and 40). A's rate is 8 units/day, B's is 9 units/day. In the last 23 days, B did 23 * 9 = 207 units. The remaining 153 units (360 - 207) were done by A and B together. Their combined rate is 17 units/day. Thus, they worked together for 153 / 17 = 9 days.