Question 10
To square a number ending in $5$, multiply the preceding number by its successor and append $25$. For example, $25^2=625$ because $2\times3=6$; $35^2=1225$ because $3\times4=12$; and $45^2=2025$ because $4\times5=20$. If $625\times625=1000N+625$, find $N$.
