Given ages of Rani, Glory, Pinky, and Minky are 20 yr, 15 yr, 5 yr and 8 yr

We know the formula,

 $\mathrm{Average} \left(\mathrm{A}\right)=\frac{\mathrm{Sum} \mathrm{of} \mathrm{given} \mathrm{values} \left(\mathrm{S}\right)}{\mathrm{Total} \mathrm{number} \mathrm{of} \mathrm{values} \left(\mathrm{N}\right)}$

 Here,

 Sum of given ages (S)

= 20+15+5+8

= 48

Total number of (N)= 4

Substituting these ages we get (A),

 $= \frac{48}{4}=12$

Hence, Option A is correct.