Quantitative | Re: Overview of GMAT Math Question Types and Patterns on the GMAT

An alarm of a certain clock rings every 20 minutes. If the clock's alarm first rings at 15:20, when will the 12th alarm of the clock ring?

A. 17:30 B. 18:00 C. 18:30 D. 19:00 E. 19:30

=>The third alarm rings at 16:00, the sixth alarm rings at 17:00. Thus every third alarm rings every hour on the hour. The 12th alarm rings at 19:00.

Ans: D

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