the number of n-digit numbers, no two consecutive digits being the same, is
a. n!
b. 9!
c. 9^n
d. n^9

there are total ten digits i.e 0 1 2 3 4 5 6 7 8 9 in the numeric system. and there are n digits in the given number. the first place can have any of the 9 digits except 0. the second place can have 9 digits as well except the digit which is at the first place. similarly the third,fourth,fifth.......nth places can also have 9 digits. so total no. of ways=9*9*9*9*9.......n times. ans:9^n