The number of different four-letter secret codes can be formed if the first letters must be an S or a T is; 35,152
How to solve permutation and combination?
If the first letters of a four-letter secret code must be an S or a T, there are 26 possible choices for the remaining two letters. This is because there are 26 letters in the alphabet, and each letter can be one of the remaining 26 letters after the first two are used.
To calculate the total number of possible combinations, you can use the following formula:
26×26×26×2.
This formula represents the number of possible combinations for each of the remaining letters. Multiplying these values together gives you the total number of possible four-letter secret codes:
26×26×26×2=35,152
So, there are 35,152 different four-letter secret codes that can be formed if the first letters must be an S or a T