Q144
ArithmeticNumber Series & Progressions
A clock strikes one at 1 o'clock, twice at 2 o'clock, ______ twelve times at 12 o'clock. How many times will the bell strike in the course of 2 days?
- a.78
- b.264
- c.312
- d.444
Answer: (C) 312
In 12 hours the clock strikes $1+2+\dots+12 = \tfrac{12\times13}{2} = 78$ times. One day has two such rounds, so $78\times2 = 156$ strikes, and two days give $156\times2 = 312$. The options 78 (only 12 hours) and 264 are traps; the question assumes the clock strikes only on the hour.