Correct Answer - Option 1 : 42
Given:
Average marks of 3 girls = 50
The ratio of the marks Girl1 ∶ Girl2 = 5 ∶ 7
Marks of Girl3 = Marks of Girl1 – 3
Formula:
Average = Sum of all observations/Total number of observations
Calculation:
Total marks of 3 girls = 3 × 50 = 150
Let the marks of Girl1 be 5x and Girl2 be 7x
Girl3 = 5x – 4
Total marks = 5x + 7x + 5x – 3
⇒ 150 = 17x – 3
⇒ 17x = 153
⇒ x = 153/17 = 9
Marks of Girl1 = 5x = 45
Girl3 = Marks of Girl1 – 3 = 45 – 3 = 42
∴ Marks of Girl3 is 42
