How many 2 digit numbers are there (using 0,9), in which the digits are not the same?
Hello guest!
10 ⇒ 19 ► 9
20 ⇒ 29 ► 9
10 ⇒ 98 ► 9 * 9 = 81
81 2 digit numbers are there, in which the digits are not the same.
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First, we calculate how many WITH repeating digits.
There are 90.
And then, we simply subtract how many repeating numbers are there. 9 numbers, 11, 22, 33, 44, 55, 66, 77, 88, 99.
90 - 9 = 81.
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