How many strings of 5 lower case english letters are there that have the letter x in them somewhere? here strings may use the same letter more than once. (hint: it might be easier to first count the strings that don't have an x in them.)

 2115751

Step-by-step explanation:

Count the number length of string of lowercase letter. one String has 26 letter.

26 letters in the lowercase.

Same as in the next string.So number of length of 5 string is = 26^5

Lets count the length of string that does not have x then string of lowercase is containing 25 letters.

25 letters and same is in the next string. So length of 5 string is = 25^5

Hence

The string of 5 lowercase letters are with at least one x = 26^5 -25^5

                                                                                             =   2115751