Handshakes again!

Probability Level 1

At a party, everyone shook hands with everybody else.

There were 15 15 handshakes.

How many people were at the party?

10 12 6 8 5

Nazmus Sakib by Nazmus sakib , 24, Bangladesh

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2 solutions

The number of handshakes ( h h ) can be given by the formula:

h = n 2 − n 2 h = \frac{n^2 - n}{2}

Evaluate the quadratic equation:

n 2 − n − 30 = 0 n^2 - n - 30 = 0

The answer can't be negative, so the answer is 6.

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1+2+3+4+5=15 last number + 1 = 5 + 1 = 6

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