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Difference between revisions of "2001 AMC 10 Problems/Problem 5"

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How many of the twelve pentominoes pictured below have at least one line of symmetry?
 
How many of the twelve pentominoes pictured below have at least one line of symmetry?
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<asy>
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unitsize(5mm);
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defaultpen(linewidth(1pt));
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draw(shift(2,0)*unitsquare);
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draw(shift(2,1)*unitsquare);
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draw(shift(2,2)*unitsquare);
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draw(shift(1,2)*unitsquare);
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draw(shift(0,2)*unitsquare);
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draw(shift(2,4)*unitsquare);
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draw(shift(2,5)*unitsquare);
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draw(shift(2,6)*unitsquare);
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draw(shift(1,5)*unitsquare);
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draw(shift(0,5)*unitsquare);
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draw(shift(4,8)*unitsquare);
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draw(shift(3,8)*unitsquare);
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draw(shift(2,8)*unitsquare);
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draw(shift(1,8)*unitsquare);
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draw(shift(0,8)*unitsquare);
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draw(shift(6,8)*unitsquare);
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draw(shift(7,8)*unitsquare);
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draw(shift(8,8)*unitsquare);
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draw(shift(9,8)*unitsquare);
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draw(shift(9,9)*unitsquare);
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draw(shift(6,5)*unitsquare);
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draw(shift(7,5)*unitsquare);
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draw(shift(8,5)*unitsquare);
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draw(shift(7,6)*unitsquare);
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draw(shift(7,4)*unitsquare);
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draw(shift(6,1)*unitsquare);
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draw(shift(7,1)*unitsquare);
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draw(shift(8,1)*unitsquare);
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draw(shift(6,0)*unitsquare);
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draw(shift(7,2)*unitsquare);
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draw(shift(11,8)*unitsquare);
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draw(shift(12,8)*unitsquare);
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draw(shift(13,8)*unitsquare);
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draw(shift(14,8)*unitsquare);
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draw(shift(13,9)*unitsquare);
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draw(shift(11,5)*unitsquare);
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draw(shift(12,5)*unitsquare);
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draw(shift(13,5)*unitsquare);
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draw(shift(11,6)*unitsquare);
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draw(shift(13,4)*unitsquare);
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draw(shift(11,1)*unitsquare);
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draw(shift(12,1)*unitsquare);
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draw(shift(13,1)*unitsquare);
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draw(shift(13,2)*unitsquare);
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draw(shift(14,2)*unitsquare);
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draw(shift(16,8)*unitsquare);
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draw(shift(17,8)*unitsquare);
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draw(shift(18,8)*unitsquare);
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draw(shift(17,9)*unitsquare);
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draw(shift(18,9)*unitsquare);
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draw(shift(16,5)*unitsquare);
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draw(shift(17,6)*unitsquare);
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draw(shift(18,5)*unitsquare);
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draw(shift(16,6)*unitsquare);
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draw(shift(18,6)*unitsquare);
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draw(shift(16,0)*unitsquare);
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draw(shift(17,0)*unitsquare);
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draw(shift(17,1)*unitsquare);
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draw(shift(18,1)*unitsquare);
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draw(shift(18,2)*unitsquare);</asy>
  
 
<math> \textbf{(A)}\ 3 \qquad \textbf{(B)}\ 4 \qquad \textbf{(C)}\ 5 \qquad \textbf{(D)}\ 6 \qquad \textbf{(E)}\ 7 </math>
 
<math> \textbf{(A)}\ 3 \qquad \textbf{(B)}\ 4 \qquad \textbf{(C)}\ 5 \qquad \textbf{(D)}\ 6 \qquad \textbf{(E)}\ 7 </math>

Revision as of 15:45, 27 April 2021

Problem

How many of the twelve pentominoes pictured below have at least one line of symmetry?

[asy] unitsize(5mm); defaultpen(linewidth(1pt)); draw(shift(2,0)*unitsquare); draw(shift(2,1)*unitsquare); draw(shift(2,2)*unitsquare); draw(shift(1,2)*unitsquare); draw(shift(0,2)*unitsquare); draw(shift(2,4)*unitsquare); draw(shift(2,5)*unitsquare); draw(shift(2,6)*unitsquare); draw(shift(1,5)*unitsquare); draw(shift(0,5)*unitsquare); draw(shift(4,8)*unitsquare); draw(shift(3,8)*unitsquare); draw(shift(2,8)*unitsquare); draw(shift(1,8)*unitsquare); draw(shift(0,8)*unitsquare); draw(shift(6,8)*unitsquare); draw(shift(7,8)*unitsquare); draw(shift(8,8)*unitsquare); draw(shift(9,8)*unitsquare); draw(shift(9,9)*unitsquare); draw(shift(6,5)*unitsquare); draw(shift(7,5)*unitsquare); draw(shift(8,5)*unitsquare); draw(shift(7,6)*unitsquare); draw(shift(7,4)*unitsquare); draw(shift(6,1)*unitsquare); draw(shift(7,1)*unitsquare); draw(shift(8,1)*unitsquare); draw(shift(6,0)*unitsquare); draw(shift(7,2)*unitsquare); draw(shift(11,8)*unitsquare); draw(shift(12,8)*unitsquare); draw(shift(13,8)*unitsquare); draw(shift(14,8)*unitsquare); draw(shift(13,9)*unitsquare); draw(shift(11,5)*unitsquare); draw(shift(12,5)*unitsquare); draw(shift(13,5)*unitsquare); draw(shift(11,6)*unitsquare); draw(shift(13,4)*unitsquare); draw(shift(11,1)*unitsquare); draw(shift(12,1)*unitsquare); draw(shift(13,1)*unitsquare); draw(shift(13,2)*unitsquare); draw(shift(14,2)*unitsquare); draw(shift(16,8)*unitsquare); draw(shift(17,8)*unitsquare); draw(shift(18,8)*unitsquare); draw(shift(17,9)*unitsquare); draw(shift(18,9)*unitsquare); draw(shift(16,5)*unitsquare); draw(shift(17,6)*unitsquare); draw(shift(18,5)*unitsquare); draw(shift(16,6)*unitsquare); draw(shift(18,6)*unitsquare); draw(shift(16,0)*unitsquare); draw(shift(17,0)*unitsquare); draw(shift(17,1)*unitsquare); draw(shift(18,1)*unitsquare); draw(shift(18,2)*unitsquare);[/asy]

$\textbf{(A)}\ 3 \qquad \textbf{(B)}\ 4 \qquad \textbf{(C)}\ 5 \qquad \textbf{(D)}\ 6 \qquad \textbf{(E)}\ 7$

Solution

Pentonimoes.gif

The ones with lines over the shapes have at least one line of symmetry. Counting the number of shapes that have line(s) on them, we find $\boxed{\textbf{(D)}\ 6}$ pentominoes.

See Also

2001 AMC 10 (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

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