Q: A, B and C can complete a work in 10, 15 and 20 days respectively. A and B start it together. B is replaced by C after 2 days. A leave it after one more day. In how many days work was completed?

• 1
  13
• 2
  \(13 {1 \over 13 }\)
• 3
  \(18 {4 \over 3 }\)
• 4
  18