Correct Answer - Option 1 : 81
Given:
Marks in 3rd exam = 87
Formula:
Average marks in N exams = Total marks in N exam/N
Calculation:
Let average score of two exams be a.
Total marks in two exams = 2a
Total marks in three exams = 2a + 87
New average = a + 3
Total marks in three exams = 3 × (a + 3) = 3a + 9
⇒ 2a + 87 = 3a + 9
⇒ a = 78
Total marks in two exams = 78 × 2 = 156
Total marks in three exams = 156 + 87 = 243
∴ Average after three exams = 243/3 = 81