'Aman' and 'Bittu' alone can do some work in 30 days and

Solution

ATQ. Let Aman, Bittu, Charu and Danny be defined as A, B, C and D respectively. Let the total work be 90 units. {LCM (30 and 45) } So, efficiency of 'A' = 90 ÷ 30 = 3 units/day And efficiency of 'B' = 90 ÷ 45 = 2 units/day And efficiency of 'C' = 2 X 2 = 4 units/day ATQ, Combined efficiency of 'A' and 'D' = Combined efficiency of 'B' and 'C' = 4 + 2 = 6 units/day So, efficiency of 'D' = 6 - 3 = 3 units/day Work done by 'A' and 'B' in 11 days = 11 X (3 + 2) = 55 units And work done by 'C' and 'D' = 90 - 55 = 35 units So, time taken by 'C' and 'D' to finish the remaining work = 35 ÷ (3 + 4) = 5 days