How many strings of 3 lower case english letters are possible that have the letter "t" in them somewhere? Here strings may use the same letter more than once?

Total possible number of strings is 26^3 (3 spaces, 26 letters each).

Total that will not include a 't' is 25^3 (3 spaces, 25 letters each).

The number that will include at least one 't' is 26^3 - 25^3

26^3 = 17,576

25^3 = 15,625

17,576 - 15,625 = 1,951