Solution:L.C.M. of 20, 25 and 30= 5 × 5 × 12 = 300 units
A's efficiency = 300/200 = 15 units.
B's efficiency = 300/25 = 12 units
C's efficiency = 300/30= 10 units.
Work finished in 3 days
= 3 × (15 + 12 + 10)
= 111 Remaining units
= 300 - 111
= 189 units Time taken by (A + C) to complete
remaining work = 189/(15+10) = 7 14/25
∴ Total time required = 3 + 7 14/25 = 10 14/25