Name: Ann
level: elementary (5th)
who: parent

A farmer takes 100 animals to the market to sell. All are sold and $100 is earned. The prices were $5.00 per cow, $1.00 per sheep and $.05 per pig. At least one of each kind of animal was sold. How many of each kind of animal did the farmer take to market?

The prices of cows and sheep are in dollars with no cents, and the amount earned is $100, with no cents. This means that the amount earned from selling the pigs must be in dollars with no cents. Since each pig costs 5 cents, the number of pigs sold must be a multiple of 20. Thus the number of pigs sold is either 20, 40, 60, 80 or 100. But we know it can't be 100 since the farmer also sold some cows and sheep. Hence the number of pigs sold is 20, 40, 60 or 80.

At this point I think you should apply the guess and check method. Would you start by guessing the number of pigs is 20 or 80?