Question

A can complete a work in 20 days and b can complete it in 30 days they both together worked for 7 days then both left it c alone completed the remaining work in 10 days how many days would be taken by c alone to complete that work

Answer 1

A can do 1/20 part of work in one day; so in 7 days A did 7/20 part

B can do 1/30 part of work in one day, in 7 days B did 7/30 part

In 7 days A+B together did 7/20+7/30=7/12 part

So work left 1-7/12=5/12

C does 5/12 part in 10 days

So C alone can do the whole work in 10*12/5=24 days

5/12 part in 10 days

1 part(whole work) in 10/5*12=24