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At some moment, Julia measured the angle between the minute and the hour hands of an a analog clock. In exactly one hour, Julia measured the angle again and got the same result. Find all possible angles.

Please solve and show work. Thanks 

 Mar 20, 2020
 #1
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Let's start off and name the angle between the hour and minute hand x, representing the number of degrees between the hands. Next, let's look at the minute hand first. After exactly an hour, the minute hand does not change its position(since after one hour, it comes back to where it was previously). As for the hour hand however, its position differs by exactly "1 hour tick", which is equivalent to 30 degrees (360 / 12 hours). What that implies is that x would have to equal x + 30, which is clearly impossible. However, we can think about the problem in a different way: by looking at the acute angle only between the hands, that would indeed be possible. Assuming that x + 30 is greater than 180(since if it wasn't, that wouldn't be possible), we can write the following equation:

 

x = 360 - (x+30) 

, with the right hand side coming from the fact that the obtuse angle of x + 30 must have an acute counterpart, of which both add up to 360. 

 

Then, we can simplify to:

 

x = 330 - x

or:

2x = 330

x = 165.

This gives us our only answer of 165 degrees

 Mar 20, 2020

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