Miss Liu has to go to the gym three times a week, but she can't go for two consecutive days to prevent excessive exercise. How many kinds of satisfaction bars does Miss Liu have?

There are 7 ways to exercise for 3 days:

C37=7×6×53×2× 1=35 (species);

Two days are arranged together as a whole, so there are still six days left. Choose two of these six days, that is, have two days together;

C26=6×52× 1= 15 (species)

35- 15=20 (type)

A: Teacher Liu has 20 classes that meet the requirements.