Query Detail : RBI Grade B Phase I

A alone can do a work in 6 days and B alone in 9 days. If C takes twice as long as A and Btogether, how long will A and C together take to complete the same work? Your Answer : 5 days Correct Answer : 4 days
Garima,   October 18th 2019,  
RBI Grade B Phase I


A            B 

6             9

LCM= 18 units

Eff of A = 3 units, Eff of B = 2 units

So C takes twice as long as A and B together So C is half efficienct of A & B together,

Eff. of C =(3+2)/2= 2.5 units

So A & C can do a job in = 18/(3+2.5) = 18/5.5 = 36/11 

Can you please tell where you find this question, we will change it.

Thanks for pointing out!