Mao Mao is the student number of the middleman.

The point is Mao Mao's student number minus 1.

Tingting is the student number of Mao Mao Jia 1.

If you add up all their students, you will find that one plus one minus one cancels out.

So the student numbers of three people add up to three times that of Mao Mao.

So the number of students in Mao Mao is 87 divided by 3=29.

Diandian's student number is 28.

Tingting's student number is 30.