Independent solution

How to solve this Counting Methods question

Setup

Setup

Choose the letter occupying the required leading position.

Nlead=26N_{\mathrm{lead}}=26

Model

Model

Select two of the four open positions for the other letters, place two different letters there, and then fill the remaining positions with digits.

Nletters=26(42)(25)(24)N_{\mathrm{letters}}=26\binom42(25)(24)
Ndigits=102N_{\mathrm{digits}}=10^2

Compute

Compute

Multiply the independent placement counts and convert the result to millions.

N=26(6)(25)(24)(100)=9,360,000N=26(6)(25)(24)(100)=9{,}360{,}000
N106=9.360\frac{N}{10^6}=9.360

Answer

Answer

The capacity is 9.360 million unique strings.

9.360 million(E)\boxed{9.360\ \text{million}\quad\text{(E)}}