Question

A person travels a certain distance with a speed of 10 km/hr and travels rest of the distance at a speed of 20 km/hr. If the total distance he travels is 15 km and all together he travels for one hour, then how much distance does he travel at a speed of 10 km/hr?

• A. 10 km
• B. 20 km
• C. 7 km
• D. 5 km

Answer 1

The correct option is D 5 km

Suppose the person travels $x$ km at a speed of 10 km/hr.
He then travels $15-x$ km distance with speed of 20 km/hr.

Total time he takes for the trip is
$\frac{x}{10}+\frac{15-x}{20}$ hr which is equal to 1 hr.

$\Rightarrow \frac{x}{10}+\frac{15-x}{20}=1\Rightarrow \frac{2x+(15-x)}{20}=1\Rightarrow \frac{x+15}{20}=1\Rightarrow x+15=20\Rightarrow x=20-15\Rightarrow x=5$

Therefore, he travels 5 km distance at a speed of 10 km/hr.