[ [ equations in integers ]

The residents of Fool City use only 35 and 80 thur bills. Can the seller make change for a buyer who wants to buy
a) a chocolate bar for 57 thurs;

b) a bun for 15 thurs?

#
a) Since both 35 and 80 are multiples of 5, the amount paid can only be a multiple of 5.

b) For example, the buyer can give the seller 5 bills of 35 tyros and receive 2 bills of 80 tyros as change.

## Answer

a) Cannot; b) can.