Question

A student rides on a bicycle at $8$ km/hour and reaches his school $2.5$ minutes late. The next day he increases his speed to $10$ km/hour and reaches the school $5$ minutes early. How far is the school from his house?

• A. $2$ km
• B. $7$ km
  
• C. $5$ km
  
• D. $15$ km
  

Answer 1

The correct option is C $5$ km

Let the distance of the school from the house = x km

Then $\frac{x}{8}-\frac{2.5}{60}=\frac{x}{10}+\frac{5}{60}\Rightarrow \frac{x}{8}-\frac{x}{10}=\frac{1}{12}+\frac{1}{24}=\frac{3}{24}=\frac{1}{8}\Rightarrow \frac{x}{40}=\frac{1}{8}\Rightarrow x=5km.$