Correct Answer - Option 4 : 80

**Given:**

The average marks of student in 5 subjects are 77.

**Formula used:**

Sum of observations = average × numbers of observations

**Calculation:**

Sum of all numbers = 77 × 5 = 385

Later, marks in one subject were increased by 15.

⇒ Correct marks = 385 + 15 = 400

∴ Correct Average = Correct sum / number = 400 / 5 = 80