A layer of oil 3 cm thick is floating on a layer of coloured water 5 cm thick. Refractive index of coloured water is `5//3` and the apparent depth of the two liquids appears to be `36//7`cm. Find the refractive index of oil.

Explanation

To solve the problem, we need to determine the refractive index of the oil layer floating on the colored water. We will use the concept of apparent depth and the formula relating real depth and apparent depth through refractive indices.

### Step-by-Step Solution:

1. **Identify Given Values**:
- Thickness of oil layer (h_oil) = 3 cm
- Thickness of colored water layer (h_water) = 5 cm
- Refractive index of colored water (n_water) = 5/3
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