Solutions
A, B and C can do a piece of work in 30 days, 40 days and 50 days, respectively.
∴ Total work = LCM of 30, 40 and 50 = 600 units
Efficiency of A = 600/30 = 20
Efficiency of B = 600/40 = 15
Efficiency of C = 600/50 = 12
Since, they work on alternate days starting with A, therefore work done by A, B and C on first, second and third day respectively are 20 units, 15 units and 12 units.
3 days → 47 units
∴ 36 days → 564 units
Work done by A on 37th day = 20 units
And, work done by B on 38th day = 15 units
Remaining work = 600 – 564 – 20 – 15 = 1 unit
Time taken by C to do a remaining work = 1/12
∴ Total time = 38 + 1/12 = 38
days
Hence, option A is the correct answer.