Mia and Ria can do a piece of work alone in 15 days and 10 days respectively. Mia started the work alone and then after 5 days Ria joined her till the completion of the work. How long did the work last?
Answer & explanation
Correct answer: option 2
Time taken ∝ $\frac{1}{efficiency}$
Mia : Ria
Time taken 15 : 10 ⇒ 3 : 2
Efficiency 2 : 3
Total Work = LCM of 10, 15 = 30
Work done by Mia in 5 days = efficiency of Mia x No. of days
= 2 x 5 = 10
Work left = 30 - 10 = 20
Efficiency of Mia and Ria together = 2 + 3 = 5
This work will taken Mia and Ria together = $\frac{work}{efficiency}$
= $\frac{20}{5}$ = 4 days
Total number of days taken to complete the work = 9 days