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How many 2 digit numbers are there (using 0,­9), in which the digits are not the same?

 Jul 26, 2017
 #1
avatar+8079 
+1

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.

 

laugh  !

 Jul 26, 2017
edited by asinus  Jul 26, 2017
edited by asinus  Jul 26, 2017
 #2
avatar+20 
+2

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.

 Jul 26, 2017

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