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