Question

Two-third of the students in a classroom are boys. If the total number of students in the class is $x$, what is the expression for the number of girls in the class?

• A. $\frac{1}{3}x$
• B. $3x$
• C. $\frac{3}{2}x$

Answer 1

The correct option is A $\frac{1}{3}x$

Total number of students in the classroom = $x$

It is given that two-third of the total number of students in the classroom are boys.
Here "of" signifies multiplication.

$\therefore$ Number of boys in the class room =
$\frac{2}{3}\text{of (Total number of students in the classroom)}$
$=\frac{2}{3}\times x$
$=\frac{2}{3}x$

$\text{Total number of girls}$$=\text{Total classroom strength}-\text{Total number of boys in the classroom}$
$\Rightarrow \text{Total number of girls}=x-\frac{2}{3}x$
$=\frac{3}{3}x-\frac{2}{3}x$
$=(\frac{3}{3}-\frac{2}{3})x$
$=\frac{1}{3}x$

$\therefore$ Expression for number of girls in the class is $\frac{1}{3}x$.