6. The integer 36 is divisible by its units digit. The integer 38 is not. How many integers between 20 and 30 are divisible by their units digit?
A 2
B 3
C 4
D 5
E 6
SOLUTION
$\mathbf{C}$

Note that 21 is divisible by 1,22 is divisible by 2,24 is divisible by 4 and 25 is divisible by 5 . However, $23,26,27,28$ and 29 are not divisible by $3,6,7,8$ and 9 respectively. Therefore there are four integers between 20 and 30 that are divisible by their units digit.