Rina can complete a piece of work in 6 days while Seema can do the same work in 9 days. If they both work together, then how many days will be required to finish the work?

Correct option is D

Given:
Rina can complete a piece of work in = 6 days
Seema can do the same work in = 9 days
Formula Used:
Work = time × efficiency
Solution:
Total work = LCM of 6 and 9 = 18 unit
Efficiency of Rina =  $$\frac{18}6$$​= 3

Efficiency of Seema = $$\frac{18}9$$​ = 2
Efficiency of Rina and Seema together = 3 + 2 = 5
Time taken by them to complete whole work  = $$\frac{18}5$$​= 3.6 days.