Solution
since each maid would work with one mop,so we shall consider 1 maid and q mop as 1 unit. Let the required time be x hours.
less maids and mops ,more time,less time (indirect proportion)
less floors,less time(direct proportion)
maida and mops 3:7::7:x
floors 7:3::7:x
3×7x=7×3×7
x=7×3×7/3×7
x=7