It can be said that you did this problem wrong because you didn't see the picture clearly. It must be noted that the ordinate is "frequency/group distance". Your teacher must have said that the ordinate of the histogram of frequency distribution is "frequency/group distance" (at least all the questions I have done are like this), and when you calculate the frequency, of course, you should use the value of the ordinate × the group distance of the abscissa, which is the frequency you want.

For example: 100, 1 10) Frequency: 0.005× 10=0.05.

1 10, 120) is 0.035× 10=0.35.