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What will be the first non-zero digit from the right in the number obtained from 347!

347! is 347 factorial

3 2 6 5 4

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1 solution

Mj Santos
Feb 1, 2015

Note that: 10 ! 10! first nonzero digit from right is 8, so if you times 1 , 2 , , 10 1,2,\ldots,10 the first nonzero digit will be 8, then 20 ! 8 2 ( m o d 10 ) 20!\equiv8^2\pmod{10} , 30 ! 8 3 ( m o d 10 ) 30!\equiv8^3\pmod{10} , \ldots , 340 ! 8 34 ( m o d 10 ) 4 ( m o d 10 ) 340!\equiv8^{34}\pmod{10}\equiv4\pmod{10}

So the first nonzero digit from right of 340 ! 340! is 4, then for 347 ! 347! , it will be the first nonzero digit from right of 347 346 345 344 333 332 331 4 7 6 5 4 3 2 1 4 347*346*345*344*333*332*331*4\equiv7*6*5*4*3*2*1*4 which is 6 \boxed6

really like your solution

Vaibhav Prasad - 6 years, 4 months ago

Is there any way other than using mod? Or please suggest me a wiki to study this modulus algorithm.

Anandhu Raj - 6 years, 4 months ago

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Modular Arithmaetic

MJ Santos - 6 years, 4 months ago

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Thankyou :)

Anandhu Raj - 6 years, 4 months ago

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