Question

A can finish a job in 15 days and B in 20 days.If they work on it together for 4 days,then the fraction of the work that is left is

Answer 1

Simple Maths,

suppose total work is 1

A=1/15 & B=1/20 for one day work

when both work together

(A+B)= (1/15)+(1/20)=7/60

for 4 days

(7/60)x4=7/15

for remaining work

1-(7/15)=8/15

Answer (8/15)

Answer 2

total work as LCM of 15 and 20,

Total work = 60 units

A finishes work in 15 days, therefore does 60/15 = 4 units in a day

B finishes work in 20 days, therefore does 60/20 = 3 units in a day

In a single day working together they finish = 4+3 = 7 units

Working together for 4 days, they will finish = 4*7 = 28 units

Part of work finished so far is = 28/total work = 28/60 = 7/15 (Ans)
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