Art of Problem Solving
AoPS Online
Math texts, online classes, and more
for students in grades 5-12.
Visit AoPS Online ‚
Books for Grades 5-12 Online Courses
Beast Academy
Engaging math books and online learning
for students ages 6-13.
Visit Beast Academy ‚
Books for Ages 6-13 Beast Academy Online
AoPS Academy
Small live classes for advanced math
and language arts learners in grades 2-12.
Visit AoPS Academy ‚
Find a Physical Campus Visit the Virtual Campus

Difference between revisions of "2006 AMC 8 Problems/Problem 23"
(→‎Video Solution by SOO)
Line 28: Line 28:
 
~Champion1234
 
~Champion1234
  
−
==Video Solution by SOO==
+
==Video Solution==
 
https://youtu.be/Gxfjwxl3Sbo Soo, DRMS, NM
 
https://youtu.be/Gxfjwxl3Sbo Soo, DRMS, NM
  

Revision as of 00:07, 16 November 2023

Problem

A box contains gold coins. If the coins are equally divided among six people, four coins are left over. If the coins are equally divided among five people, three coins are left over. If the box holds the smallest number of coins that meets these two conditions, how many coins are left when equally divided among seven people?

$\textbf{(A)}\ 0\qquad\textbf{(B)}\ 1\qquad\textbf{(C)}\ 2\qquad\textbf{(D)}\ 3\qquad\textbf{(E)}\ 5$

Solution

Solution 1

The counting numbers that leave a remainder of $4$ when divided by $6$ are $4, 10, 16, 22, 28, 34, \cdots$ The counting numbers that leave a remainder of $3$ when divided by $5$ are $3,8,13,18,23,28,33, \cdots$ So $28$ is the smallest possible number of coins that meets both conditions. Because $4\cdot 7 = 28$, there are $\boxed{\textbf{(A)}\ 0}$ coins left when they are divided among seven people.

Solution 2

If there were two more coins in the box, the number of coins would be divisible by both $6$ and $5$. The smallest number that is divisible by $6$ and $5$ is $30$, so the smallest possible number of coins in the box is $28$ and the remainder when divided by $7$ is $\boxed{\textbf{(A)}\ 0}$.

Solution 3

We can set up a system of modular congruencies: \[g\equiv 4 \pmod{6}\] \[g\equiv 3 \pmod{5}\] We can use the division algorithm to say $g=6n+4$ $\Rightarrow$ $6n\equiv 4 \pmod{5}$ $\Rightarrow$ $n\equiv 4 \pmod{5}$. If we plug the division algorithm in again, we get $n=5q+4$. This means that $g=30q+28$, which means that $g\equiv 28 \pmod{30}$. From this, we can see that $28$ is our smallest possible integer satisfying $g\equiv 28 \pmod{30}$. $28$ $\div$ $7=4$, making our remainder $0$. This means that there are $\boxed{\textbf{(A)}\ 0}$ coins left over when equally divided amongst $7$ people.

~Champion1234

Video Solution

https://youtu.be/Gxfjwxl3Sbo Soo, DRMS, NM

Video Solution

https://youtu.be/g1PLxYVZE_U -Happytwin

https://www.youtube.com/watch?v=uMBev3FUoTs ~David

See Also

2006 AMC 8 (Problems • Answer Key • Resources)
Preceded by
Problem 22 		Followed by
Problem 24
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25
All AJHSME/AMC 8 Problems and Solutions

The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. AMC logo.png

Retrieved from "https://artofproblemsolving.com/wiki/index.php?title=2006_AMC_8_Problems/Problem_23&oldid=203841"