SOLUTION: Christi's mother gave her $9.00 to buy 10 cent and 15 cent stamps. Christi returned with $1.75 in change and a total of 60 stamps. How many of each kind of stamp did she buy?

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Question 147686: Christi's mother gave her $9.00 to buy 10 cent and 15 cent stamps. Christi returned with $1.75 in change and a total of 60 stamps. How many of each kind of stamp did she buy?
Answer by mangopeeler07(462) About Me  (Show Source):
You can put this solution on YOUR website!
-----With two variables: # of 10 cent stamps is x. # of 15 cent stamps is y. You have the prices of the stamps and the sum of the price of 60 stamps. So first set up an equation x%2By=60. Then set up 10x%2B15y=725. Then in the first equation solve for x. You should get x=60-y. Plug that in the second equation and get 10%2860-y%29%2B15y=725. Distribute the ten and get 600-10y%2B15y=725. Combine like terms 600%2B5y=725. Subtract 600 from both sides and get 5y=125. Then divide by five and y=25. Then plug in y in the original equation and get x=35. So she bought 35 10cent stamps and 25 15 cent stamps.


-----With one variable: Also, you could start out with 10x%2B15%2860-x%29=725 since you know the sum to be 60. Then distribute and get 10x%2B900-15x=725. Combine like terms and get -5x%2B900=725. Subtract 900 from each side and get -5x=175. Divide by -5 and get x=-35. Now, you can't buy a negative amount of stamps, so make 35 positive. x=35. Then plug x into the original equation and get y=25. So she bought 35 10cent stamps and 25 15 cent stamps.