The number of committees of five persons with a chair person can be selected from 12 persons,

A chair person can be selected in 12 ways

Now, we need to select 4 person out of remaining 11.

∴ Number of committees of five person with a chair person can be selected in 12 × 11C4 ways

i.e $12 \times \frac{11 !}{4 ! 7 !}$

$=\frac{12 \times 11 \times 10 \times 9 \times 8}{4 \times 3 \times 2}$

$=3960$