<image>In order to understand the physical fitness of the students, some students from a certain grade of a school were selected to take a one-minute jump rope test. After organizing the data, a frequency distribution histogram was drawn as shown in the figure. It is known that the frequencies of the three groups from left to right in the figure are 0.1, 0.2, and 0.4, respectively. The frequency of the first group is 5. Then the frequency of the fourth group is equal to ___ . 