Difference between revisions of "2015 AMC 8 Problems/Problem 15"
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Revision as of 22:28, 29 November 2023
Contents
Problem
At Euler Middle School, students voted on two issues in a school referendum with the following results:
voted in favor of the first issue and
voted in favor of the second issue. If there were exactly
students who voted against both issues, how many students voted in favor of both issues?
Solutions
Solution 1
We can see that this is a Venn Diagram Problem.
First, we analyze the information given. There are students. Let's use A as the first issue and B as the second issue.
students were for A, and
students were for B. There were also
students against both A and B.
Solving this without a Venn Diagram, we subtract away from the total,
. Out of the remaining
, we have
people for A and
people for B. We add this up to get
. Since that is more than what we need, we subtract
from
to get
.
Solution 2
There are people. We know that
people voted against both the first issue and the second issue. That leaves us with
people who voted for at least one of them. If
people voted for both of them, then that would leave
people out of the vote, because
is less than
people.
is
, so to make it even; we have to take
away from the
people, which leaves us with
.
Solution 3
Divide the students into four categories:
- A. Students who voted in favor of both issues.
- B. Students who voted against both issues.
- C. Students who voted in favor of the first issue and against the second issue.
- D. Students who voted in favor of the second issue and against the first issue.
We are given that:
.
.
students voted in favor of the first issue.
students voted in favor of the second issue.
We can quickly find that:
students voted against the second issue.
students voted against the first issue.
so
The answer is .
Solution 4 (PIE)
Using PIE (Principle of Inclusion-Exclusion), we find that the students who voted in favor of both issues are .
~MrThinker
Video Solution (HOW TO THINK CRITICALLY!!!)
~Education, the Study of Everything
Video Solution
https://youtu.be/OOdK-nOzaII?t=827
~savannahsolver
See Also
2015 AMC 8 (Problems • Answer Key • Resources) | ||
Preceded by Problem 14 |
Followed by Problem 16 | |
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 |
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