The marks scored by Rohit in two tests were 65 and 70.

Let x be the minimum  marks he scores in the third test.

Then, $\frac{65+70+x}{3} \geq 65$

$\Rightarrow \frac{135+x}{3} \geq 65$

$\Rightarrow 135+x \geq 195 \quad$ (Multiplying both the sides by 3$)$

$\Rightarrow x \geq 195-135$

$\Rightarrow x \geq 60$

Hence, the minimum marks Rohit should score in the third test should be 60 .