The average marks of 50 students in a class is 72. The average marks of boys and girls in that subject are 70 and 75 respectively. The number of boys in the class is
Options:
A . 25
B . 30
C . 35
D . 20
Answer: Option B Answer: (b)Number of students in the class = x (let) ∴ Number of girls = 50 – x According to the question, x × 70 + (50 – x) × 75 = 50 × 72 ⇒ 70x + 3750 – 75x = 3600 ⇒ 3750 – 5x = 3600 ⇒ 5x = 3750 – 3600 = 150 ⇒ x = $150/5$ = 30
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