Minutes of Courtyard Bell

Welcome! You are encouraged to register with the site and login (for free). When you register, you support the site and your question history is saved.

In a courtyard, one bell rings every hour and other bell rings every hour. Both bells ring together exactly at the beginning of each hour. Which of the following gives all of the intervals that occur between any two rings of a bell, in minutes?

Review: Minutes of Courtyard Bell


Explanation

In this question, one bell rings every 15 minutes and the other rings every 12 minutes, and they are synchronized on the hour. So the minutes of the rings of the first bell are 0, 15, 30, 45, and 60. The minutes of the second bell's rings are 0, 12, 24, 36, 48, and 60. Combining them, the rings happen at

0, 12, 15, 24, 30, 36, 45, 48, 60

Comparing our list with the answer choices: there are intervals of 3, so (A) is out. There are no intervals of 15, so (C) is out. There are intervals of 12, so (B) is out. We are left with (D) and (E). From 36 to 45 is 9 minutes.

The correct answer is (D).


If you believe you have found an error in this question or explanation, please contact us and include the question title or URL in your message.
Continue »