Question

Hello! Can someone help me, please? Thank you so much!

Topic: possibility.

How many double digit numbers are there where the two digits are different from each other ?

Answer 1

81

Explanation:

double digit numbers begin at 10 and end at 99

10 → 19 has 10 double digits

20 → 29 has 10 double digits

and so on up to 90 → 99

that is there are 90 double digits from 10 → 99

double digits with same value are 11, 22, 33, 44, 55, 66, 77, 88, 99

that is 9 double digits with the same value

Then double digits with different values = 90 - 9 = 81

Answer 2

81 double digits numbers.

Explanation:

From 1 to 99, first 9 numbers are single digit numbers

Double digit numbers = 99 - 9 =90

In this 90 numbers, 11,22,33,44,55,66,77,88,99 have same digits.

90 - 9 = 81