Give a general algorithm/formula for finding the power ai

Hi, I've this is my homework I've been given and I can only manage part i) and iii)

http://img535.imageshack.us/img535/7...ersproblem.png

My work for part

i)

2x(3^2)

iii)

A zero appears at the end of the solution (as we go from 1! to 400!) every time we cross a number ending in 5 and every time we cross a number ending in 0.

Two zeros appear every time we cross a number ending in 50 and every time we cross a number ending in 00, However, this includes numbers already counted above (beware of double counting.

Number of numbers ending in "5" : 40

Number of numbers ending in "00" : 4 (100, 200, 300, 400)

Number of numbers ending in "50" : 4 (50, 150, 250, 350)

Number of remaining numbers ending with one "0" : 32 = 4*8 (10, 20, 30, 40, 60, 70, 80, 90 for each hundred).

Expected number of zeros at the end of the number = 40 + 8 + 8 + 32 = 88