100 persons had food provision for 24 days. If 20 persons left the place, the provisions will last for

∵ 100 persons had food provision for 24 days.

∴ 1 person had food provision for 24 × 100 i.e. 2400 days

If 20 persons left the place, then remaining persons = (100-20) = 80

∴ 80 persons had food provision for

Hence, option (a) is correct.