8 salesmen sell 50 box of shoes working 20 hours a day, then how many boxes of shoes can be sold when 24 salesmen work for 30 hours a day?
More salesmen means more boxes can be sold, so it is in direct proportion. The proportion is 8:24∷50:x
If more hours spend, then more boxes can be sold, so it is in direct proportion. The proportion is 20:30∷50:x
We know that the product of extremes = the product of means.
8×20×x=24×50×30
x=(24×50×30)/(8×20)=225