Nine
Level
pending
Is 123456789999999 divisible by nine? Solve without calculator
No
Yes
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A number is divisible by 9 if and only if the sum of its digits are divisible by 9. Consider 2 different parts of the number, 12345678 and 9999999.
1+2+3+4+5+6+7+8 = 8(9)/2, which is divisible by 9. 9+9+9+9+9+9+9 = (9)(7), which is divisible by 9.
Clearly, the sum of these 2 parts is divisible by 9, so the sum of all the digits is divisible by 9.
Thus, 123456789999999 is divisible by 9.