2023 AMC 8 Problems/Problem 14
Problem
Nicolas is planning to send a package to his friend Anton, who is a stamp collector. To pay for the postage, Nicolas would like to cover the package with a large number of stamps. Suppose he has a collection of 20 of each of 5 cent, 10 cent, and 25 cent stamps. What is the GREATEST number of stamps that Nicolas can use to make exactly 7.10 in postage?
Written Solution
Most stamps make 
You have 20 of each coin, nickles, dimes and quarters.
If we want to have the most amount of stamps we have to have the most amount of smaller value coins. We can use 20 nickels and 29 dimes to bring our total cost to 
. However when we try to use quarters the 25 cents don’t fit evenly, so we have to give back 15 cents in order to make the quarter amount 4.25 the most efficient way to do this is give back a dime and a nickel to have 38 coins used so far. Now we just use 
quarters to get a grand total of 
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Solution
The maximum amount of money in postage he can make with his collection of stamps is 20(5+10+25) = 800 cents, or 8 dollars. To make 7.10 in postage, he should subtract 90 cents, while removing the lowest number of stamps. To do this, he should remove as many 25 cent stamps as possible. He can remove at most 3 such stamps. After that, he will have exactly 7.25 left, and the way to remove 15 cents from that while removing the least number of stamps is by removing 1 10 cent stamp and 1 5 cent stamp. That will make 7.10 in postage, and he will have removed 5 total stamps: 3 25 cent stamps, 1 10 cent stamp, and 1 5 cent stamp. Since he has 20(3) = 60 stamps in his entire collection, the number of stamps used is 20(3) - 5 = 55, so the answer is E.
pianoboy
Animated Video Solution
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