Answers

2016-04-24T03:39:45+05:30
After 7 days A did 7/14=1/2 piece of work, and B 7/21=1/3 piece. The remaining work:
1 - 1/2 - 1/3 = 6/6 - 3/6 - 2/6 = 1/6 worked B in 21 * 1/6 = 3.5 days.
The work was in 7 + 3.5 = 10.5 days completed.

Answer: 10.5 days

Note: If A had not been ill, it's the work would be finished by x days:
x/14 + x/21 = 1
3x/42 + 2x/42 = 1
5x = 42
x = 8.4 days
0