Solutions
Given:
A can complete the work in 10 days
B can complete the work in 15 days
C can complete the work in 30 days
A and B started to work and after 3 days B left and C joined A on the work.
Formula used:
The efficiency of a person is the inverse of the time taken
Calculation:
Per day efficiency of A and B together = 1/10 + 1/15 = 1/6
Per day efficiency of A and C together = 1/10 + 1/30 = 2/15
Total work done by A and B in 3 days = 3 × (1/6) = 1/2
Total work remaining = 1 - 1/2 = 1/2
Let the A and C take n days to complete the remaining work
⇒ n × (2/15) = 1/2
⇒ n = 3.75
∴ Total time taken = 3 + 3.75 = 6.75 days