Coins

Edmund had saved a certain number of 2-euro coins. He placed the coins in a single layer in a square. He had 6 coins left. When he wanted to build a square with one more row, he was missing 35 coins.
How many euros does he have?

Correct answer:

n =  812 Eur

Step-by-step explanation:

$$\begin{gathered} n=2\cdot x \\ x\cdot x+6=(x+1)(x+1)-35 \\ 6=2x+1-35 \\ x=20 \\ n=2\cdot (20\cdot 20+6)=812\text{Eur} \end{gathered}$$

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