Difference between revisions of "2017 AMC 10A Problems/Problem 5"
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Revision as of 17:25, 8 March 2017
Contents
Problem
The sum of two nonzero real numbers is 4 times their product. What is the sum of the reciprocals of the two numbers?
Solution
Let the two real numbers be 
. We are given that 
and dividing both sides by 
, 
![\[\frac{1}{y}+\frac{1}{x}=\boxed{\textbf{(C) } 4}.\]](http://latex.artofproblemsolving.com/e/a/1/ea1dadbf53587b5968e46e59c6f61f87125eeed4.png)
Note: we can easily verify that this is the correct answer; for example, 1/2 and 1/2 work, and the sum of their reciprocals is 4.
Solution 2
Instead of using algebra, another approach at this problem would be to notice the fact that one of the nonzero numbers has to be a fraction.
See for yourself. And by looking into fractions, we immediately see that 
and 
would fit the rule. 
See Also
| 2017 AMC 10A (Problems • Answer Key • Resources) | ||
| Preceded by Problem 4 |
Followed by Problem 6 | |
| 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 | ||
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions. 
