Let $n=1 !+4 !+7 !+\ldots+400 !$. Then ten's digit of $n$ is
Let $n=1 !+4 !+7 !+\ldots+400 !$. Then ten's digit of $n$ is
1
6
2
7
Solution
Given, $n=1 !+4 !+7 !+\ldots+400 !$ $1 !=1,4 !=24,7 !=5040,10 !=3628800$ and further the terms has last two digits $=00$
So,
$1 !+4 !+7 !+\ldots+400 !=\ldots \ldots 65$
Here ten digit is 6 .
Hence, 6 is the answer.