Question

If passwords may contain lower case letters and digits, how many 6-character passwords start with the lower case letter 'a' or ends with the number '3'? Answer:

Answer 1

Solution 1-

The password is of six characters.

First character will be 'a' and last is '3' . So these positions are fixed and we need to find the number of combinations keeping this in mind . Letters 'a-z' and '0-9' are total 36 in number.

Now we can fill second position with any 36 characters, for the third position also we can fill it will any of 36 characters, for fourth and fifth also we can fill them with any of the 36 characters because the numbers or digits can be repeated any number of time.

So finally we have-

First place- 1 choice ...i.e a

second place- 36 choices

third place-36 choices

fourth place-36 choices

fifth place-36 choices

sixth place-1 choice i.e 3

so Total number of combinations are 1*36*36*36*36*1=1679616