QUESTION

CSAT

Hard

Maths

Prelims 2014

A bell rings every 18 minutes. A second bell rings every 24 minutes. A third bell rings every 32 minutes. If all the three bells ring at the same time at 8 o'clock in the morning, at what other time will they all ring together?

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Explanation

To find when all three bells ring together again, we need to calculate the Least Common Multiple (LCM) of the given time intervals:

The first bell rings every 18 minutes. The second bell rings every 24 minutes. The third bell rings every 32 minutes. Step 1: Prime Factorization 18=2×3218 = 2 \times 3^2 24=23×324 = 2^3 \times 3 32=2532 = 2^5

Step 2: Find LCM The LCM is found by taking the highest powers of each prime factor: The highest power of 2 is 252^5 (from 32). The highest power of 3 is 323^2 (from 18). Thus, LCM = 25×32=32×9=2882^5 \times 3^2 = 32 \times 9 = 288 minutes.

Step 3: Convert Minutes to Hours and Minutes 288 minutes = 4 hours 48 minutes.

Step 4: Add to Initial Time The bells first ring together at 8:00 AM. Adding 4 hours 48 minutes to 8:00 AM gives 12:48 PM.

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