Study Break - Quiz: The Problem that will get you into Harvard

Colleges and Universities A-Z Harvard University
21

<p>I'm not sure if this is a solution, but:</p>

<p>The original poster stated that "any change to a scale is considered a move." Therefore, if the scale does not change, then it does not count toward a weighing."</p>

<p>Therefore:</p>

<p>1st weighing
First, take any two coins and place them on the two sides of the scale. If it is balanced, then take two more coins and add one of each to each side. If it still is balanced, add the last two coins in the same fashion to each side. One of these three tries will result in an unbalanced scale.</p>

<p>2nd weighing
When an unbalance is discovered, take the last two coins added on and take one of them (the one in question) and weigh it against another coin (not the other one added at the same time), and if they are balanced then the other coin (added the same time as the one in question) is the fake. If they are not balanced, then that coin (the coin in question) is the fake coin. </p>

<p>Although it might seem like there are a lot of weighings altogether, there is actually only two, for if the scale doesn't change, then it is not considered a "move."</p>

22

<p>Hey lukeli88, your solution seems to be the most satisfactory one I've read so far. The OP defined a move as a change in the scale so i guess your argument is good.</p>

23

<p>im a hunior so no i didnt but this is good preperation for when i have an interview. i love this website for all its usefulness.</p>

24

<p>You won't be asked a question like this for college interviews...</p>