Question

a,b,c can complete a job in 10 15 and 20 days respectively . a abd b starts to work together but after 2 days b leaves. the left work is done by a and c how long will they take to do so

Answer 1

A in 10 days ------- 1 part
A in 1 day --------- 1/10 part

B in 15 days -------- 1 part
B in 1 day --------1/15 part

C in 20 days -------- 1 part
C in 1 day ---------- 1/20 part

A+B in 1 day ---- 1/10 + 1/15
= (3+2)/30
= 1/6

A+B in 2 days ----- 1/6 × 2 = 1/3

Work left = 1 - 1/3
= 2/3

A+C in 1 day -------- 1/10 + 1/20
= (2+1)/20
= 3/20

A+C do 3/20 part in 1 day
A+C do 1 part in 20/3 days
A+C do 2/3 part in 20/3 × 2/3 days
= 40/9 days
= 4-4/9 days

Answer 2

A can comete a job-10days
time taken by A to complete the work=1/10days
B can comete a job-15days
time taken by B to complete the work-1/15days
C can complete a job-20days
time taken by C to complete the work-1/20days
(A+B) 1 day work-(1/10+1/15)=(3+2/30)=(5/30)=1/6
(A+B) 2 days work-(1/6*2)=1/3
remaining work-(1-1/3)=2/3
(A+C) 1 day work-(1/10+1/20)=(2+1/20)=3/20
=(3/20*2/3)=1/10days
(A+C)can complete the work-10days.

HOPE THIS HELPS YOU