The ratio of efficiency of A, B and C is 7: 5: 8, together they can complete a work in 42 days. B and C worked together for 21 days and A did the remaining work alone, then find how long it took to complete the work?
-
102
-
81
-
87
-
75
-
None of these
A
Correct answer
Explanation
Efficiency ratio 7:5:8. Total units/day = 20. In 42 days, total work = 840 units. B+C (13 units/day) work for 21 days: 13 × 21 = 273 units. Remaining work = 840 - 273 = 567 units done by A alone (7 units/day). Time for A = 567/7 = 81 days. Total time = 21 + 81 = 102 days. This matches option A.