sandy wrote:
A certain vent releases steam every 20 minutes. If the vent releases steam at 6:25 p.m., which of the following could be a time at which the vent releases steam?
A. 9:15 p.m.
B. 10:40 p.m.
C. 11:00 p.m.
D. 12:20 p.m.
E. 1:05 a.m.
Since the vent releases steam every 20 minutes, and we are given that it releases steam at 6:25 pm, we we that whatever time it will release steam, the time must have 5 as the “last” digit. Therefore, we can eliminate choices B, C and D.
Now let’s write couple more times the vent will release steam after 6:25 pm:
6:45 pm, 7:05 pm, 7:25 pm, 7:45 pm, 8:05 pm, …
We see that if we only focus on the minutes and not the hour, the time the vent releases steam is always at X:45, X:05 and X:25. Therefore, only choice E can be the correct answer.
Answer: E