2012 AMC 10B Problem 4

Below is the professionally curated solution for Problem 4 of the 2012 AMC 10B, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2012 AMC 10B solutions, or check the answer key.

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Concepts:modular arithmetic

Difficulty rating: 770

4.

When Ringo places his marbles into bags with 6 marbles per bag, he has 4 marbles left over. When Paul does the same with his marbles, he has 3 marbles left over. Ringo and Paul pool their marbles and place them into as many bags as possible, with 6 marbles per bag. How many marbles will be left over?

1 1

2 2

3 3

4 4

5 5

Solution:

As we know that when Ringo's marbles are divided by 6,6, we have a remainder of 4,4, we conclude that he has 6x+46x+4 marbles for some x.x.

Using the same logic, we can also conclude that Paul has 6y+36y+3 marbles for some y.y.

Therefore, the total number of marbles is (6x+4)+(6y+3)(6x+4)+(6y+3) =6(x+y+1)+1= 6(x+y+1)+1 which, when divided by 6,6, only leaves 11 left over.

Thus, the correct answer is A .

Problem 4 in Other Years