Kathy needs to mail a gift card to a friend. She uses 48-cent stamps and 7-cent stamps to pay $2.55 in postage. How many of each stamp did Kathy use?

Answer 1

48x + 7y = 255

You must guess and check to solve this because you have just one equation and two unknowns.

If x = 1, then y = 29.57, which is not a whole number.

If x = 2, then y = 122.71, which is not a whole number.

If x = 3, then y = 15.86, which is not a whole number.

If x = 4, then y = 9, which a a whole number. This is a solution.

If x = 5, then y = 2.14, which is not a whole number.

If x = 6, then y = a negative number, so not a solution.