Two point charges are placed at separation `d` in vacuum and the force between them is `F`. Now a dielectric slab of thickness `t = d//3` and dielectric constant `K` is placed between the charges and the force becomes `9F//25`. Find the value of `K`.

Explanation

To solve the problem step by step, we will use the concepts of electrostatics, particularly Coulomb's law and the effect of a dielectric on the force between two charges.

### Step 1: Understanding the Initial Condition
Initially, we have two point charges \( q_1 \) and \( q_2 \) separated by a distance \( d \) in a vacuum. The force between them is given by Coulomb's law:

\[ F = \frac{k \cdot |q_1 \cdot q_2|}{d^2} \]
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