Difference between revisions of "2011 AMC 12B Problems/Problem 23"
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<math>-4 + x\le y \le 4 - x</math> | <math>-4 + x\le y \le 4 - x</math> | ||
− | So for <math>x = 4</math>, there are <math>13</math> | + | So for <math>x = 4</math>, there are <math>13</math> lattice points, |
− | for <math>x = 5</math>, there are <math>11</math> | + | for <math>x = 5</math>, there are <math>11</math> lattice points, |
etc | etc | ||
− | for <math>x = 8</math>, there are <math>5</math> | + | for <math>x = 8</math>, there are <math>5</math> lattice points. |
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Revision as of 22:32, 23 December 2011
Problem
A bug travels in the coordinate plane, moving only along the lines that are parallel to the -axis or -axis. Let and . Consider all possible paths of the bug from to of length at most . How many points with integer coordinates lie on at least one of these paths?
Solution
Answer: (C)
If a point satisfy the property that , then it is in the desire range because is the shortest path from to , and is the shortest path from to
If , then satisfy the property. there are lattices points here.
else let (and for it is symmetrical, ,
So for , there are lattice points,
for , there are lattice points,
etc
for , there are lattice points.
Hence, there are a total of lattice points.
See also
2011 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 22 |
Followed by Problem 24 |
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 |