A cook bought 100 pounds of rice. If he used 4/5 of it in cooking, how many pounds of rice did he use?
From “used 4/5 of it in cooking” the word after “used 4/5 of” is “it” or “100 pounds of rice” so the amount rice bought is the amount in 1 (whole).
4/5 of 100 pounds of rice were used in cooking so we multiply the amount in 1 ( whole ), 100 pounds, with the fractional part used,4/5 , to find the amount in this part, the amount of rice used:
4/5x 100=80 pounds