Summer Clouds moderators
16/07/2017 at 12:30-
There are \(9\) digits could be the ones digits: \(0,1,2,3,4,5,6,7,8,9.\)
If the ones digit is \(0\) then there are: \(9-0=9\left(numbers\right)\) satisfy the question.
If the ones digit is \(1\) then there are: \(9-1=8\left(numbers\right)\) satisfy the question.
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If the ones digit is \(9\) then there are: \(9-9=0\left(numbers\right)\) satisfy the question.
So there are total: \(9+8+7+6+5+4+3+2+1+0=45\left(numbers\right)\) satisfy the question.
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Trần Nhật Dương 16/07/2017 at 17:12There are 99 digits could be the ones digits: 0,1,2,3,4,5,6,7,8,9.
If the ones digit is 00 then there are: 9−0=9(numbers) satisfy the question.
If the ones digit is 11 then there are: 9−1=8(numbers) satisfy the question.
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If the ones digit is 99 then there are: 9−9=0(numbers) satisfy the question.
So there are total: 9+8+7+6+5+4+3+2+1+0=45(numbers) satisfy the question