All possibilities = 9!
possibilities that harry sits at an end = 8! + 8!
possibilities that harry doesn't sit at an end = 9! - 8! -8!
Difference means you want to find the change between two, thus u subtract between both of it.
m-2
In your question, 45 is not a perfect square.
A perfect square is when you divide or multiply the number by itself.
36 is a perfect square because it's factor is 6 x 6 (6,6).
<span>64 is a perfect square because it's factor is 8 x 8 (8,8).
</span><span>81 is a perfect square because it's factor is 9 x 9 (9,9).</span>
