Question

A can do a certain job in 25 days which B alone can do in 20 days . A srtated the work and was joined by B after 10 days . In how many days was the whlole work completed ?

Answer 1

A can do a certain job in 25 days
so, percentage of A's work for one day = 100%/25 = 4%

B can do in 20 days
so, percentage of B's work for one day = 100%/20 = 5%

A started the work and B joined after 10 days
so A alone do the work for 10 days

so, percentage of A's work for 10 days = 4% × 10 = 40%

so, A alone do 40% work in 10 days and the remaining 60% work done by both A and B

so, A and B complete 60% work in x days
x(A+B) = 60%
x(4% + 5%) = 60%
9%x = 60%
x = 60%/9%
x = 6.666 days

so A and B work together to complete 60% work in 6.66 days

whole work completed in 10 + 6.66 = 16.66 days