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.