6. How many positive integers between 100 and 300 have only odd digits?
A 25
B 50
C 75
D 100
E 150
SolUTion
A

For each digit to be odd, the first digit has to be 1 , the second digit can be any one of $1,3,5,7$ or 9 and so can the third digit. Hence the number of positive integers between 100 and 300 with only odd digits is $1 \times 5 \times 5=25$.