Difference between revisions of "2012 AMC 8 Problems/Problem 9"
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Revision as of 15:34, 3 July 2013
Problem
The Fort Worth Zoo has a number of two-legged birds and a number of four-legged mammals. On one visit to the zoo, Margie counted 200 heads and 522 legs. How many of the animals that Margie counted were two-legged birds?
Solution
Let the number of two-legged birds be 
and the number of four-legged mammals be 
. We can now use systems of equations to solve this problem.
Make two equations:
Now multiply the latter equation by 
.
Using cancellation, we find that 
. Since there were 
heads, meaning that there were animals, there were 
two-legged birds.
See Also
| 2012 AMC 8 (Problems • Answer Key • Resources) | ||
| Preceded by Problem 8 |
Followed by Problem 10 | |
| 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 | ||
These problems are copyrighted © by the Mathematical Association of America, as part of the American Mathematics Competitions. 
