To create an entry​ code, you must first choose 2 letters and​ then, 4 ​single-digit numbers. How many different entry codes can you​ create?

Answer 1

For the first position you choose a letter out of 26.

For each choice of the first position you can again choose a letter for the

second position in 26 way.

That gives you 26×26 options for the first two positions.

For each of those you can choose a digit for the third position in 10 ways.

That gives you 26×26×10 ways of selecting the first three positions.

You continue in this way filling in the other positions with digits,

which in the end gives you

26×26×10×10×10×10 = 6,760,000

possible codes.