Christi's mother gives her $9.00 to buy $0.10 and $0.15 stamps. christi returned with $1.75 in change and a total of 60 stamps. how many of each kind of stamp did she buy ?

Information Given

Total Cost of the stamps = $9.00 - $1.75 = $7.25
Total number of stamps = 60
Value of the $0.10 stamp = $0.10
Value of the $0.15 stamp = $0.15


Assumed all $0.10 stamps.

Assumed all the 60 stamps she bought were $0.10 stamps.
$0.10 x 60 = $6.00


Find amount not accounted for.

Amount of money not accounted for:
$7.25 - $6.00 = $1.25

The $1.25 must had been used to pay for the $0.15 stamps.


Find difference in values between the two stamps.

Difference in the value of the two stamps:
$0.15 - $0.10 = $0.05


Find number of $0.15 stamps

Number of $0.15 stamps = $1.25 ÷ $0.05 = 25
There were 25 $0.15 stamps.


Find number of $0.10 stamps.

Number of $0.10 stamps = 60 - 25 = 35
There were 35 $0.10 stamps.


35 $0.10 stamps and 25 $0.10 stamps.