There are ten kids in a class. when any two meet, each says “hi” to the other and the answer “hi” follows. before the class starts, how many times would one hear the word “hi”?

If every single student met one an another, then you would hear 90 hi's. Since there are 45 different combinations of 2 students meeting another, and since there are 2 hi's each meeting, there would be 90.

I hope that this helps.

Please rate me as Brainliest so I can rank up :D