Question

How many strings of length 5 can be made using the letters " ABCDE" which start with A and in which CD always comes together?

1 * 3!*2!

Answer 1

$$3!2!=12$$

$$ABCDE, ABECD, ACDBE,$$

$$ACDEB, AECDB, AEBCD,$$

$$ABDCE, ABEDC, ADCBE,$$

$$ADCEB, AEDCB, AEBDC$$