Consider the alphabet Σ = {A, B, C, D, E, F, G}. How many different strings of length 4 can be generated from the letters in Σ that contain a single G and a single A, with G preceding A?
Consider the alphabet Σ = {A, B, C, D, E, F, G}. How many different strings of length 7 can be generated from the letters in Σ that begin or end with a vowel?