Choose 2 out of 5 students, and * * * has C52= 10.

There are three possibilities to choose a boy (i.e C3 1).

Because there is only one boy, there are two kinds of other girls (C2 1).

The above is gradual, so any boy has 3*2=6 kinds.

So the probability of just a boy is 6/ 10=3/5.

The opposite of at least one boy is that there are no boys, that is, all girls.

There are only two girls in a room, so there is only one possibility.

So the probability of at least one boy among the participating students is:

1- 1/ 10=9/ 10