Question

A bell rings every 18 seconds, another every 60 seconds. At 5.00 pm the two ring simultaneously. At what time will the bells ring again at the same time

Answer 1

Prime factors of 18: 2, 3, 3

Prime factors of 60: 2, 2, 3, 5

So, take the maximum number of times each factor is used and multiply them together

2x2x3x3… and multiply by any other factors that aren’t used… 5

2x2x3x3x5 = 180

So 180 minutes after 5 pm will be the next time both bells ring. 180 minutes = 3 hours.

8pm.