Pawan completes 40% of a task in 6 days. His efficiency is 100% greater than Qureshi's. How many days will it take for both Pawan and Qureshi, working together, to finish the entire task?

ATQ,
Pawan’ alone can do the complete work in (6/0.4) = 15 days
Efficiency of ‘Pawan’ = 2 × efficiency of ‘Qureshi’
As, we know efficiency is inversely proportional to time taken when work done is constant.
So, ‘Qureshi’ alone can complete the work = (15 × 2) = 30 days
Let the total work be 30 units {LCM of 15 and 30}
Efficiency of ‘Pawan’ = (30/15) = 2 units/day
Efficiency of ‘Qureshi’ = (30/30) = 1 unit/day
So, time taken by ‘Pawan’ and ‘Qureshi’ to complete the work together = (30/3) = 10 days