If $\frac{x^{2}-1}{x^{2}+1} \geq 0,$ then $x \in$

Let $m, n$ be real numbers such that $0 \leq m \leq \sqrt{3}$ and $-\sqrt{3} \leq n \leq 0$. The minimum possible area of the region of the plane consisting of points $(x, y)$ satisfying the inequalities $y \geq 0$,$y - 3 \leq mx$,and $y - 3 \leq nx$ is

The number of integral values of $x$ satisfying $5x - 1 < (x + 1)^2 < 7x - 3$ is

The $IQ$ of a person is given by the formula $IQ = \frac{MA}{CA} \times 100$,where $MA$ is mental age and $CA$ is chronological age. If $80 \leq IQ \leq 140$ for a group of $12$ years old children,find the range of their mental age.

$A$ solution of $8 \%$ boric acid is to be diluted by adding a $2 \%$ boric acid solution to it. The resulting mixture is to be more than $4 \%$ but less than $6 \%$ boric acid. If we have $640$ litres of the $8 \%$ solution,how many litres of the $2 \%$ solution will have to be added?

The water acidity in a pool is considered normal when the average pH reading of three daily measurements is between $8.2$ and $8.5$. If the first two pH readings are $8.48$ and $8.35$,then find the range of $pH$ value for the third reading that will result in the acidity level being normal.