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Question 886171: Ann purchased 19 stamps, a mixture of 49 cents and 20 cents stamps. Find the numbers of each type of stamp if she spent $7.28.
Answer by jgr45(31)   (Show Source):
You can put this solution on YOUR website! Let x = the number of 49¢ stamps, and y = the number of 20¢ stamps; and I will express the money in cents (i.e. total of 728¢ was spent).
So we have a two equation system:
49x + 20y = 728, and
x + y = 19.
We need to isolate a variable (I'll pick y)
y = 19 - x
Now substitute 19-x for y in the first equation:
49x + 20(19-x) = 728
49x + 380 - 20x = 728
29x + 380 = 728
29x = 348
x = 12
Which means y = 19-12, or 7.
Plug these values into first equation:
49(12) + 20(7) =? 728
588 + 140 = 728
728 = 728 {{check}}
So Ann bought 12 49¢ and 7 20¢ stamps with her $7.28 .
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