Question

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”?

Answer 1

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.

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Answer 2

Hello!

This is kind of like combinations. You are pairing two kids to basically say hi to each other. :) Since there are 10 kids in class, let's calculate this!

2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 20

or 

10 x 2 = 20 

I hope this helps! If it doesn't, please let me know. Cheers and have a lovely day!