1.

The remainder when `1!+2!+3!+4!+......+1000!` is divided by `10` is

Answer» Given expression is = `1!+2!+3!+4!+5!...+1000!`
`1! = 1`
`2! = 2**1=2`
`3! = 3**2**1 = 6`
`4! = 4**3**2**1 = 24`
`5! = 5**4**3**2**1 = 120`
So, `5!` is divisible by `10`.
Now, `6! = 6**5!`
So, `6!` will also be divisible by `10`.Similarly, every term greater than `5!` in the given expression will be divisible by `10`.
So, sum of the terms that are not divisible by `10` is,
`1!+2!+3!+4! = 1+2+6+24 = 33`
`:.` Remainder of `33` when divided by `10` will be `3` which is the required answer.


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