Answer
1/4
Work Step by Step
P(event)=$\frac{numberoffavorableoutcomes}{numberofpossibleoutcomes}$
There are 20 differences between the stem and leaf plot so this is the number of possible outcomes. Out of the 20, five are more than 20 points:(23, 27, 72, 35, 45) so this is the number of favorable outcomes.
So, the probability is:
P(more than 20 points)=$\frac{5}{20}$ -simplify-
P(more than 20 points)=$\frac{1}{4}$