Each with each

Five pupils from 3A class played table tennis. How many matches did they play with each other?

Correct answer:

n =  10

Step-by-step explanation:

$$\begin{gathered} z=5 \\ n={\displaystyle \frac{z\cdot (z-1)}{2}}={\displaystyle \frac{5\cdot (5-1)}{2}}=10 \end{gathered}$$

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