# Dollar Bills and system of two linear equations

by Kendall Whiteside
(Happy Valley, Oregon)

“A student has some \$1 bills and \$5 bills in his wallet. He has a total of 15 bills that are worth \$47. How many of each type of bill does he have? ”

Let x be the number of \$1 bills and y be the number of \$5 bills.

The number of \$1 bills plus the number of \$5 bills equal 15 or x + y = 15

Worth of \$1 bills plus worth of \$5 bills = \$47 or 1x + 5y = 47

Therefore, just solve the system of equations below.

x + y = 15 (1)

x + 5y = 47 (2)

(2) minus (1) will give 4y = 32

y = 8 since 4 × 8 = 32

x + 8 = 15

x = 7

The student has seven \$1 bills and eight \$5 bills.

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