Please explain the solution of this Question:- "If the real depth of a coin in water (µ = 4/3) is  4 cm, the apparent depth is?" 

This is the simplest question based on refractive index directly based on the formula. It is highly recommended that you cover the topics given in the study matter.

Refractive index (μ) = (Real Depth)/(Apparent Depth) 

or 4/3 = 4/Apparent Depth

thus, apparent depth = 3cm