What is the last non - zero digit in (20!)!? (That is, factorial of 20 factorial).

(In reply to simple solution by Tristan)

I see how the last non-zero digit of 10! will be the last non-zero digit of the product of the last non-zero digits of 10,9,8,7,...2,1 namely (1*2*3*...*9*1=8), but how is the product of the last non-zero digits from 11-20 equal to that of 10!? (1*2*3*...*9*2=6)!?. Similarly the last non-zero digit of the product of the last non-zero digits from 21-30 would be (1*2*3*...*9*3=4) except that we have multiplied by 25 along the way nullifying the effect of another one of our 2's making the last non-zero digit of 30! = 8*6*2=6

What I can see is that 20! ends in 80000. Maybe I am missing something...
Edited on December 22, 2003, 6:29 am

Posted by Eric on 2003-12-22 06:22:29