A Psychologist Is Interested in How Well People Can Remember

Multiple Choice

A psychologist is interested in how well people can remember words that they had previously seen.He gives them a list of 70 words,but does not tell them they will be tested later.One week later the students are given a list of 140 words,and told to choose the ones they had seen the previous week.Below is the grouped distribution of the number of words remembered by the subjects.
What is the score at the 50^th percentile?

A) 20
B) 22
C) 23
D) 37