UPSC CDS 1 2021 Math Paper

let a person can clean 1 unit of floor in one day. then,
20 persons clean 20 floors ≡20 days
20 persons clean 1 floor ≡1 day
1 person cleans 1 floor ≡20 days
1 person cleans 16 floors ≡20×16 days =320 days
16 persons clean 16 floors ≡

320

16

days =20 days