Elga is 20 years old and Alvin would be 5. Hope this helped.
Solution : Given points to be fill are : 5 external points + 5 internal points
Total positions to be fill are 5+5 = 10
given number of sea shell to be placed are = 10
Here all sea shell are different so each sea shell is different from any other sea shell
if we interchange the position of any two sea shell we would be getting totally different
arrangement .
We can think this problem like 10 sea shell are to be placed at 10 different places
We start with placing first sea shell .
In the beginning we have 10 positions
once it is placed we pick second sea shell and now we have only 9 vacant places
once it is placed we pick next ses shell and we have 8 vacant places for it
we continue with it till we place the last sea shell for which we would be having
only 1 vacant place.
This way the total number of arrangements we get : 10x9x8x7x6x5x4x3x2x1 = 3628800
ANSWER = 3628800
The missing length is M = 15
