How many days are required by Priya to clean the house, if Mona can do it in 5 days and together they can complete in 3 days.

Correct option is A

Given:
Mona can clean the house in = 5 days
Mona + Priya can do it together in = 3 days
Formula Used:
work = time × efficiency
Solution:
Total Work = LCM of 3 and 5 = 15 unit
Efficiency of Mona = $$\frac{15}{5} = 3$$ unit per day
Efficiency of Mona and Priya together = $$\frac{15}{3} = 5$$​ unit per day
Efficiency of Priya = Efficiency of Mona + Priya - efficiency of Mona = 5 - 3 = 2
Time required for Priya to finish work = $$\frac {15}2$$​ = 7.5 days