Difference between revisions of "2009 AMC 10B Problems/Problem 15"
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Since <math>a</math> is one bucket plus two-thirds of the total amount of water, and <math>b</math> is one bucket plus one-half of the total amount of water, <math>a-b</math> would equal <math>\cancel{\text{bucket}}+\frac23\cdot\text{water}-(\cancel{\text{bucket}}+\frac12\cdot\text{water})=\frac16\cdot\text{water}</math>. Therefore, <math>a-b</math> is one-sixth of the total mass of the water. Starting from <math>a</math>, we add two one-sixths of the total amount of the water to become full. Therefore, the full bucket of water is <math>a+2(a-b)=a+2a-2b=3a-2b\Rightarrow\textbf{(E)}</math> | Since <math>a</math> is one bucket plus two-thirds of the total amount of water, and <math>b</math> is one bucket plus one-half of the total amount of water, <math>a-b</math> would equal <math>\cancel{\text{bucket}}+\frac23\cdot\text{water}-(\cancel{\text{bucket}}+\frac12\cdot\text{water})=\frac16\cdot\text{water}</math>. Therefore, <math>a-b</math> is one-sixth of the total mass of the water. Starting from <math>a</math>, we add two one-sixths of the total amount of the water to become full. Therefore, the full bucket of water is <math>a+2(a-b)=a+2a-2b=3a-2b\Rightarrow\textbf{(E)}</math> | ||
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== Video Solution == | == Video Solution == |
Latest revision as of 10:31, 19 January 2021
- The following problem is from both the 2009 AMC 10B #15 and 2009 AMC 12B #8, so both problems redirect to this page.
Contents
Problem
When a bucket is two-thirds full of water, the bucket and water weigh kilograms. When the bucket is one-half full of water the total weight is kilograms. In terms of and , what is the total weight in kilograms when the bucket is full of water?
Solution
Solution 1
Let be the weight of the bucket and let be the weight of the water in a full bucket. Then we are given that and . Hence , so . Thus . Finally . The answer is .
Solution 2
Imagine that we take three buckets of the first type, to get rid of the fraction. We will have three buckets and two buckets' worth of water.
On the other hand, if we take two buckets of the second type, we will have two buckets and enough water to fill one bucket.
The difference between these is exactly one bucket full of water, hence the answer is .
Solution 3
We are looking for an expression of the form .
We must have , as the desired result contains exactly one bucket. Also, we must have , as the desired result contains exactly one bucket of water.
At this moment, it is easiest to check that only the options (A), (B), and (E) satisfy , and out of these only (E) satisfies the second equation.
Alternatively, we can directly solve the system, getting and .
Solution 4
Since is one bucket plus two-thirds of the total amount of water, and is one bucket plus one-half of the total amount of water, would equal . Therefore, is one-sixth of the total mass of the water. Starting from , we add two one-sixths of the total amount of the water to become full. Therefore, the full bucket of water is
Video Solution
See also
2009 AMC 10B (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 AMC 10 Problems and Solutions |
2009 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 7 |
Followed by Problem 9 |
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 AMC 12 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.