There are 100 students in 3 sections A, B and C of a class.

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There are 100 students in 3 sections A, B and C of a class. The average marks of all the 3 sections was 84. The average of B and C was 87.5 and the average marks of A is 70. The number of students in A was

1. 30
2. 35
3. 20
4. 25

Correct Option: C

Number of students in section A = n
∴ Number of students in sections B and C = (100 – n)
∴ n × 70 + (100 – n) × 87.5 = 84 × 100
⇒ 70n + 87.5 × 100 – 87.5n = 8400
⇒ 8750 – 17.5n = 8400
⇒ 17.5n = 8750 – 8400 = 350

⇒ n =	350	= 20
	17.5