Question

How many two-digit counting numbers do not contain any of the digits 1, 3, or 9?

42 numbers

72 numbers

81 numbers

49 numbers

Answer 1

Two-digit number,

case 1. we can not include 0, 1 3 9 then remaining number if 2,4,5,6,7,8

the number of remaining numbers is 6, with the help of 6 numbers we can create 6*6=36 possible number of two-digit.

without zero 36 numbers are possible.

case 2. take zero and fixed it at first digit,

....0

remaining one digit fill by 2,4,5,6,7,8,

6 possible way (20,40,50,60,70,80)

(02,04, is not a two-digit number. it is a single-digit number)

in this case, we get 6 possible ways.

The total possible number is (6+36)=42