2018 · Q42
The minute hand of a clock overtakes the hour hand after every 72 minutes of correct time. How much time does the clock lose or gain in a day of normal time ?
Elementary MathematicsTime, Speed and Distance
- ALose 121 911/{9}{11}
- BLose 157 111/{1}{11}
- CGain 121 911/{9}{11}
- DGain 157 111/{1}{11}
Explanation
The hands of a correct clock coincide every 65 5/11 minutes, so a clock on which they coincide every 72 minutes of correct time is running slow. As printed, the question is defective: the true daily loss is 1440/11 = 130 10/11 minutes, which is not among the options. The setter-intended (official) key is 'Lose 121 9/11', i.e. option A, but this key is disputed. (key disputed)