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