Find the remainder when 1 ! + 2 ! + 3 ! + … + 1 0 0 ! is divided by 24.
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4 ! is 2 4 , then, for n ! ≥ 4 , 2 4 ∣ n ! that means its remainder is 0
So
( 1 ! + 2 ! + 3 ! + … … + 1 0 0 ! ) ≡ ( 1 ! + 2 ! + 3 ! + 0 + . . . + 0 ) m o d 2 4
( 1 ! + 2 ! + 3 ! + … … + 1 0 0 ! ) ≡ 9 m o d 2 4
∴ remainder is 9
By careful observation, we get that 2 4 1 ! + 2 ! + 3 ! + . . . . 1 0 0 ! = 2 4 1 ! + 2 ! + 3 ! + 2 4 4 ! + 5 ! + . . . . + 1 0 0 !
We know that any number above 4 ! is divisible by 2 4 so 2 4 4 ! + 5 ! + . . . . + 1 0 0 ! has a remainder of 0
We need to take care of the first fraction: f r a c 1 ! + 2 ! + 3 ! 2 4 , which leaves a remainder of 9
LOL the title of the question is a clue HAHAAH
24 is a factor of 4!, 5!, 6!.......100!. Therefore remainder is 1! +2! +3! = 1+2+6 = 9 Even if the series continued to infinity answer would have been the same.
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As we know
4 ! = 2 4 , 5 ! = 2 4 × 5 , 6 ! = 2 4 × 6 × 5 . . . . . . . . . .
Means every number starting from 4 ! will give us remainder as 0 on dividing by 2 4
Means we will get remainder from 1 ! + 2 ! + 3 ! = 9
and 2 4 m o d 9 = 9
∴ the answer is ⇒ 9