Art of Problem Solving

2002 AMC 10A Problems/Problem 21: Difference between revisions

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==Problem==
==Problem==
A set of tiles numbered 1 through 100 is modified repeatedly as follows: remove all tiles numbered with a perfect square, and renumber the remaining tiles consecutively starting with 1. How many times must the operation be performed to reduce the number of tiles in the set to one?
The mean, median, unique mode, and range of a collection of eight integers are all equal to 8. The largest integer that can be an element of this collection is


<math>\text{(A)}\ 10 \qquad \text{(B)}\ 11 \qquad \text{(C)}\ 18 \qquad \text{(D)}\ 19 \qquad \text{(E)}\ 20</math>
<math>\text{(A)}\ 11 \qquad \text{(B)}\ 12 \qquad \text{(C)}\ 13 \qquad \text{(D)}\ 14 \qquad \text{(E)}\ 15</math>


==Solution==
==Solution==

Revision as of 09:18, 27 December 2008

Problem

The mean, median, unique mode, and range of a collection of eight integers are all equal to 8. The largest integer that can be an element of this collection is

$\text{(A)}\ 11 \qquad \text{(B)}\ 12 \qquad \text{(C)}\ 13 \qquad \text{(D)}\ 14 \qquad \text{(E)}\ 15$

Solution

Given $n^2$ tiles, a step removes $n$ tiles, leaving $n^2 - n$ tiles behind. Now, $(n - 1)^2 = n^2 - n + (1 - n) < n^2 - n < n^2$, so in the next step $n - 1$ tiles are removed. This gives $(n^2 - n) - (n - 1) = n^2 - 2n + 1 = (n - 1)^2$, another perfect square, and the process repeats.

Thus each two steps we cycle down a perfect square, and in $(10 - 1)\times 2 = 18$ steps, we are left with $1$ tile.

See Also

2002 AMC 10A (ProblemsAnswer KeyResources)
Preceded by
Problem 20
Followed by
Problem 22
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