On mixing two classes A and B of students having average

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On mixing two classes A and B of students having average marks 25 and 40 respectively, the overall average obtained is 30. Find the ratio of the students in the class A and B.

1. 2 : 1
2. 5 :8
3. 5 : 6
4. 3 : 4

Correct Option: A

Number of students in class A = x
Number of students in class B = y
∴ 25x + 40y = 30(x + y)
⇒ 25x + 40y = 30x + 30y
⇒ 30x – 25x = 40y – 30y
⇒ 5x = 10y

⇒	x	=	10	= 2 : 1
	y		5