Question

If there are forty new students in a class and the students have to shake each others hand once, how many hand shakes will occur?

Pleas help me i am confused.............:(:(

i need a formula

Answer 1

Each student shakes 39 hands.

40 * 39 = ?

Answer 2

so that would be 1560.....but my teacher want a formula so that it can work with any other number....please help

Answer 3

x(x - 1) = y