Question

Of the 2 digit num( those from 11 to 95 both inclusive) how many having second difit greater than first digit

Answer 1

20,30,40,50,60,70,80,90 have first digit greater. So we will not consider them.

From 11 to 19 ==> 8 numbers (except 11)

From 21 to 29 ==> 7 numbers (except 21,22)

From 31 to 39 ==> 6 numbers (except 31,32,33)

From 41 to 49 ==> 5 numbers (except 41,42,43,44)

From 51 to 59 ==> 4 numbers (except 51,52,53,54,55)

From 61 to 69 ==> 3 numbers (except 61,62,63,64,65,66)

From 71 to 79 ==> 2 numbers (except 71,72,73,74,75,76,77)

From 81 to 89 ==> 1 number (except 81,82,83,84,85,86,87,88)

From 91 to 95 ==> 0 ( 91,92,93,94,95 all have first digit greater)

So total = 8+7+6+5+4+3+2+1+0 = 36 numbers

Answer 2

Answer:

36

Step-by-step explanation:

As the units digit (second digit) has to be greater than 10s digit (first digit),-

For 8 being first digit second digit will be 9 (1 number)

First digit 7 --> second digit 8 or 9 (2 numbers)

... ...

First digit 2 --> second digit 3 to 9 (7 numbers)

First digit 1 --> second digit 2 to 9 (8 numbers)

Total numbers = 8+7+6+5+4+3+2+1 = 8(8+1)/2 = 36