Call Letters In 1923, the Federal Communications Commis- sion directed that all new radio stations east of the Mississippi River have call letters beginning with the letter W. How many different three- or four-letter call letters are possible

30

three- or four-letter call letters are possible.

Step-by-step explanation:

three- or four-letter call letters that are possible will be 3 factorial plus 4 factorial

3! + 4!

3! = 3 ×2 ×1 = 6

4! = 4 × 3 × 2 × 1 = 24

3! + 4! = 6 + 24 = 30

Note that in Probability, or means +