The perimeter of a square is numerically equal to its area. The perimeter of the square is :

1. 4 units

2. 8 units

3. 12 units

4. 16 units

If the width of the uniform shaded portion is x m; its area in terms of x is :

1. 320 m² - (16 - 2x)(20 - 2x) m²

2. 320 m² - (16 - x)(20 - x) m²

3. 320 m² - (16 - 2x)(20 - x) m²

4. 320 m² - (16 - x)(20 - 2x) m²

The speed of train A is x km/hr and speed of train B is (x - 5) km/h. How much time will each train take to cover 400 km ?

1. $\dfrac{x}{400} \text{ hrs and } \dfrac{x - 5}{400}$ hrs

2. x × 400 hrs and (x - 5) × 400 hrs

3. $\dfrac{400}{x} \text{ hrs and } \dfrac{400}{x - 5}$ hrs

4. $\dfrac{800}{x(x - 5)}$ hrs

A boy is twice as old as her sister. Four years hence, the product of their ages (in years) will be 160. Find their present ages.