SOLUTION: A shopper brought 35 stamps in 25-cent and 15-cent denominations. If the total spent on the stamps was $7.05, how many 15-cent stamps were bought?
Question 1002794: A shopper brought 35 stamps in 25-cent and 15-cent denominations. If the total spent on the stamps was $7.05, how many 15-cent stamps were bought? Answer by ikleyn(52788) (Show Source):
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A shopper 35 stamps in 25-cent and 15-cent denominations. If the total spent on the stamps was $7.05, how many 15-cent stamps were bought?
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Answer. 18 stamps in 25 cents and 17 stamps in 15 cents.
Solution
Let us assume for a minute that all the stamps are in 15 cents each.
Then the total cost would be 35*15 = 525 cents = $5.25, which is in $1.80 less than $7.05.
It is clear that the difference is due to presence of $0.25 stamps that we intently counted as $0.15.
It is also clear that the number of these $0.25 stamps is = = 18 to compensate the difference.
It gives the answer: 18 stamps in 25 cents and 35-18 = 17 stamps in 15 cents.
There is another method to solve this problem using equations or systems of equations.
The way that I used here allows you to solve the problem using the mental math only.
