6 December 2015

Arithmetic & Algebraic Problems - AT RIGHT ANGLES

Question: Rackbrane asked his young friends at the breakfast table one morning this little question:
"How soon between the hours of five and six will the hour and minute hands of a clock be exactly at right angles?"

Answer: To be at right angles the minute hand must always be exactly fifteen minutes either behind or ahead of the hour hand. Each case would happen eleven times in the twelve hours-i.e., every 1 hour 5 5/11 minutes. Starting from nine o'clock, the eighth addition will give the case 5 hours 43 7/11 minutes. In the other case, starting from three o'clock, the second addition gives 5 hours 10 10/11 minutes.

These are the two cases between five and six, and the latter will, of course, be the sooner.

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