The average marks of boys in a class is 52 and that of girls is 42. The average marks of boys and girls combined is 50. The percentage of boys in the class is
JEE · Math · previous-year question
- A.80correct
- B.60
- C.40
- D.20
Answer
A. 80
Explanation
Let x and y are number of boys and girls in a class respectively. $$\therefore$$ 52x + 42y = 50 (x + y) $$ \Rightarrow$$ 52x + 42y = 50x + 50y $$ \Rightarrow$$ 2x = 8y $$ \Rightarrow$$ x = 4y $$\therefore$$ Total no. of students = x + y = 4y + y = 5y $$\therefore$$ Percentage of boys = $${{4y} \over {5y}} \times 100\,\% $$ = 80%
Practice more JEE questions
Answer thousands more real JEE previous-year questions free, get graded instantly, and climb the global ranked leaderboard.
Practice JEE free →More JEE Math questions
- What is the total number of distinct x \in \mathbb{R} for which \left|\begin{array}{ccc}x …
- Let m be the smallest positive integer such that the coefficient of x^{2} in the expansion…
- What is the total number of distinct x \in[0,1] for which \int_{0}^{x} \frac{t^{2}}{1+t^{4…
- Let \alpha, \beta \in \mathbb{R} be such that \lim _{x \rightarrow 0} \frac{x^{2} \sin (\b…
- Let z=\frac{-1+\sqrt{3} i}{2}, where i=\sqrt{-1}, and r, s \in\{1,2,3\}. Let P=\left[\begi…
- For how many values of p, the circle x^{2}+y^{2}+2 x+4 y-p=0 and the coordinate axes have …
- Let f: \mathbb{R} \rightarrow \mathbb{R} be a differentiable function such that f(0)=0, f\…
- For a real number \alpha, if the system \[ \left[\begin{array}{ccc} 1 & \alpha & \alpha^{2…