Abir does 80% of a work in 20 days. He then calls in Belal and they together finish the remaining work in 3 days. How long Belal alone would take to do the whole work?

Question: Abir does 80% of a work in 20 days. He then calls in Belal and they together finish the remaining work in 3 days. How long Belal alone would take to do the whole work?

Solution:
abir does 80% or 4/5 work in 20 days
in one day, he does 1/25 work
in 3 days, he does 3/25 work

work remaining = 1/5 - 3/25
= 2/25 work

Belal does 2/25 parts in 3 days
he will complete the work 75/2 days