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Number Theory Level 2

The sum of digits of 23 ! 23 ! is

Example:

5 ! = 5 × 4 × 3 × 2 × 1 = 120 5 ! = 5 \times 4 \times 3 \times 2 \times 1= 120

the sum in this case is 1 + 2 + 0 = 3 1 + 2 + 0 = 3 .

105 56 43 99 64

Mehdi K. by Mehdi K. , 24, Iraq

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1 solution

Clearly, 9 ∣ 23 ! 9|23! , then the sum of the digits of 23 ! 23! is divisible by 9 9 . In the given options, there's only one number that is divisible by 9 9 , which is 99 99 .

1 Helpful 0 Interesting 0 Brilliant 0 Confused

How do you know it must be 99? Can't it be 90?

Pi Han Goh - 5 years ago

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Your question has point

Dev Rajyaguru - 5 years ago

He seems to have eliminated other options

Shreyansh Mukhopadhyay - 3 years, 4 months ago

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