factorial problem

find the first non-zero digit in 80!?

4 Answers

1057
Ketan Chandak ·

i knw a method...
first find all the prime factors of the required no nd den multiply the units digit of each of the factors....
but dats too tedius.....ne better method?

1057
Ketan Chandak ·

first digit from the right i meant...

7
Sigma ·

@Ketan: I also know that method which u r talking about . find the prime factors divide by1019. . then taking the last digit of the remaining factors, multiplying them and getting the last digit of the product as the answer to the q.

3
h4hemang ·

hmmm.
take modulo 10 after removing the powers of 10.

visit this link.

http://www.mathpages.com/home/kmath489.htm

here is a past year problem in AMC and its solution.
http://www.artofproblemsolving.com/Wiki/index.php/2010_AMC_10A_Problems/Problem_24

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