Chapter 22 - Reflection and Refraction of Light - Learning Path Questions and Exercises - Exercises - Page 775: 27

$66.7$%

From Exercise 25, apparent depth $d^{'}=\frac{d}{n}$ where d is the actual depth. So, required percentage $=\frac{\frac{d}{n}}{d}\times100=\frac{100}{n}$ For oil , n=1.5 Hence. required percentage $=\frac{100}{1.5}=66.7$%