Question

3) Aaron and his friend Bobby went school shopping and bought pens &

pencils. Each pen costs $3 and each pencil costs $2. They bought a total
of 7 items for $18. How many pens did they buy?

Answer 1

3 pens.

Explanation:

x+y=7 where x is # of pens and y =# of pencils

3x + 2y= $18

from first equation, x=-y+7 so substitute that into other equation

3(-y+7)+2y=18

-3y+21+2y=18

-y=18-21

-y=-3

y=3

now replace y =3 into first equation

x+3=7

x=4