Difference between revisions of "2023 AMC 8 Problems/Problem 14"

Revision as of 22:40, 23 November 2023

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 $5$ -cent, $10$ -cent, and $25$ -cent stamps, with exactly $20$ of each type. What is the greatest number of stamps Nicolas can use to make exactly $$7.10$ in postage? (Note: The amount $$7.10$ corresponds to $7$ dollars and $10$ cents. One dollar is worth $100$ cents.)

$\textbf{(A)}\ 45 \qquad \textbf{(B)}\ 46 \qquad \textbf{(C)}\ 51 \qquad \textbf{(D)}\ 54\qquad \textbf{(E)}\ 55$

Solution 1

Let's use the most stamps to make $7.10.$ We have $20$ of each stamp, $5$ -cent (like nickels), $10$ -cent (like dimes), and $25$ -cent (like quarters).

If we want to have the highest number of stamps, we have to have the highest number of the smaller value stamps (like the coins above). We can use $20$ nickels and $20$ dimes to bring our total cost to $7.10 - 3.00 = 4.10$ . 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 to give back a $10$ -cent (dime) stamp and a $5$ -cent (nickel) stamp to have $38$ stamps (coins) used so far. Now, we just use $\frac{425}{25} = 17$ quarters to get a grand total of $38 + 17 = \boxed{\textbf{(E)}\ 55}$ .

~apex304, SohumUttamchandani, wuwang2002, TaeKim, Cxrupptedpat

Solution 2

The value of his entire stamp collect is $8$ dollars. To make

$$7.10$ with stamps, he should remove $90$ cents worth of

stamps with as few stamps as possible. To do this, he should

start by removing as many $25$ cent stamps as possible as

they have the greatest denomination. He can remove at most

$3$ of these stamps. He still has to remove $90-25\cdot3=15$

cents worth of stamps. This can be done with one $5$ and $10$

cent stamp. In total, he has $20\cdot3=60$ stamps in his

entire collect. As a result, the maximum number of stamps he

can use is $20\cdot3-5=\boxed{\textbf{(E)}\ 55}$ .

~pianoboy

~MathFun1000 (Rewrote for clarity and formatting)

Video Solution (CREATIVE THINKING!!!)

https://youtu.be/vq3voJZ-hvw

~Education, the Study of Everything

Video Solution by Math-X (Smart and Simple)

https://youtu.be/Ku_c1YHnLt0?si=GHLp1q_7Le68a4rJ&t=2454 ~Math-X

Animated Video Solution

https://youtu.be/XP_tyhTqOBY

~Star League (https://starleague.us)

Video Solution by Magic Square

https://youtu.be/-N46BeEKaCQ?t=4280

Video Solution by Interstigation

https://youtu.be/DBqko2xATxs&t=1435

Video Solution by harungurcan

https://www.youtube.com/watch?v=VqN7c5U5o98&t=449s

~harungurcan

@@ Line 55: / Line 55: @@
 https://youtu.be/-N46BeEKaCQ?t=4280
 ==Video Solution by Interstigation==
-https://youtu.be/1bA7fD7Lg54?t=1078
+https://youtu.be/DBqko2xATxs&t=1435
 ==Video Solution by harungurcan==

2023 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 13	Followed by Problem 15
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