Question

Class XII of XYZ International School has three sections K, L, and M. In Mathematics examination, the average marks obtained by these sections are 72, 60 and 50 respectively. The average marks of sections K and L taken together is 69. If the ratio of the number of students in sections Land M is 6: 7, what is the average score of all the three sections put together?

Options

• 65

• 64

• 63.4

• 64.7

Answer 1

64.7

Explanation:

Let the number of students in sections K, L and M are n, 6x and 7x respectively.

Then, total number of students in
Section K = 72 × n = 72 n
Section L = 60 × 6x = 360 x
Section M = 50 × 7x = 350x

Average marks of section K and L

`=("Sum of marks of section K and L")/("total number of students of K and L")`

`69 =(72"n"+360"x")/("n"+6"x")`

69n + 414x = 72n + 360x

3n = 54x

n = 18x

Number of students in section K =18x .

Average marks of three sections

`=(72xx18"x"+360"x"+350"x")/(18"x"+6"x"+7"x")=(2006"x")/(31"x")=64.7`