What is the mode of this data set: 17, 13, 18, 20, 17, 15, 12

A. 19

B. 17

Answer: B. 17

The mode is the most frequent or most occurring value. The value 17 shows up the most times, at two times, so this is the mode. The value 19 is not even part of the given set of values, so you can immediately cross of choice A.

Side note: it is possible for a set to have more than one mode, and it's also possible to not have a mode at all.