Answer:
81
Step-by-step 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:
81 double digits numbers.
Step-by-step 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
