rate of A = 1/a
and rate of B = 1/b
if a starts work it completes in 1,2 , 5,6 , 9,10 = 6 days
and b in 3,4 , 7,8 ; 4 days
6/a + 4/b = 1---(1)
and if b starts work we will have b rate ; 6/b and a ends with half day more ; 4.5/a
6/b+4.5/a=1--(2)
solve for 1 &2
we get
a=9 and b = 12
so combined rate = 1/9+1/12 = 7/36
36 /7 days IMO D
Bunuel wrote:
Working alone at their respective constant rates, A can complete a task in ‘a’ days and B in ‘b’ days. They take turns in doing the task with each working 2 days at a time. If A starts they finish the task in exactly 10 days. If B starts, they take half a day more. How long does it take to complete the task if they both work together?
A. 46/9
B. 50/9
C. 50/11
D. 36/7
E. 210/41
Are You Up For the Challenge: 700 Level Questions