1) You can only go once a day. You can't go once in the morning, once in the evening and once at noon. In that case, three times may be one day, so you can't think about it. In other words, you go to the gym three days a week;
2) The days when you go to the gym with your classmates are random. If you go on Monday, Tuesday and Wednesday, and your classmates go on Thursday and Friday, the probability of meeting each other is zero.
3) Suppose you can meet each other as long as you go to the gym on the same day. If you go early and he goes late, you won't miss it.
When your classmate chooses two days out of seven days, C (2,7) = 21;
Because you account for three of them, there are only six situations in which classmates don't meet you.
The probability that you meet your classmates is 1-6/2 1=5/7.