Question

A man walks from his house to his dougther's school at a speed of $3$km/hr and return back at speed of $4$ km/hr. If he takes $21$ minutes for the double journey; find the distance between his house and the school.

• A. $0.7km.$
• B. $0.2km.$
• C. $0.6km.$
• D. $0.9km.$

Answer 1

The correct option is C $0.6km.$

Let the distance between house and school $=D$ km

Since, Time $=\frac{Distance}{Speed}$
$\frac{D}{3}+\frac{D}{4}=\frac{21}{60}$
$\frac{7D}{12}=\frac{21}{60}$
$=>D=\frac{3}{5}=0.6km$