Question

A can do a piece of work in 80 days. He works at it for 10 days and then B alone finishes the
remaining work in 42 days. In how many days could both do it?

Answer 1

we see that a completes worlnin 80 days

so he workd at that piece of work for 10 days

which means 70 days work remains

b finishes it in 42 days

it means b is 1.66x of a speed

now let us calculate the speed of b if the whole work to be done by him

the answers come 48 days

now we know how many days it would take for a and b to complete their work alone

now 1/48 + 1/80

5/240 + 3/240

8/240

1/30

they both can complete 1/30 of the work in 1 day

1 upon 30/1 days

30 days is ur answer