Ajay and Vijay can finish a task in 9 days working

Solution

ATQ,

Let the Ajay, Vijay and Charu can be define as A, B and C respectively.

Let total amount of work be 18 units {LCM of (9 and 18)}

Efficiency of ‘A’ and ‘B’ together = (18/9) = 2 units/day

Efficiency of ‘C’ alone = (18/18) = 1 units/day

Given, Efficiency of ‘C’ = 2 × efficiency of ‘B’

So, efficiency of ‘B’ = 0.5 units/day

So, efficiency of ‘A’ = (2 – 0.5) = 1.5 units/day

Work done by ‘A’ and ‘C’ together in 4 days = 4 × (1.5 + 1) = 10 units

Remaining work = 18 – 10 = 8 units

So, 8 units of work will be completed by ‘A’, ‘B’ and ‘C’ together in = {8/(1.5 + 0.5 + 1)} = (8/3) days

Therefore, total time taken to complete the work = 4 + (8/3) = (20/3) days