Ravi obtained 70 and 75 marks in first two unit test. Find the minimum marks he should get in the third

Let x be the marks obtained by Ravi in the third unit test.

Since the student should have an average of at least 60 marks,

$\frac{70+75+x}{3} \geq 60$

$\Rightarrow 145+x \geq 180$

$\Rightarrow x \geq 180-145$

$\Rightarrow x \geq 35$

Thus, the student must obtain a minimum of 35 marks to have an average of at least 60 marks.