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

Then, (70 + 75 + x)/3 ≥ 60

⇒ 145 + x ≥ 180 ⇒ x >180 – 145

⇒ x ≥ 35

Thus, Ravi must obtain a minimum of 35 marks to get an average of at least 60 marks.

**Note:** A minimum of 35 marks.

⇒ Marks greater than or equal to 35.