Question

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

• A. 2.7 km
• B. 3.4 km
• C. 0.6 km
• D. 1.6 km

Answer 1

The correct option is C 0.6 km

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

Since, Time $=\frac{Distance}{Speed}$

$\frac{D}{3}+\frac{D}{4}=\frac{21}{60}$

$\frac{7D}{12}=\frac{21}{60}$

$D=\frac{3}{5}=0.6km$