A car covers a distance of 240 km. If its speed is increased by 20 km/h, the travel time decreases by 1 hour. What was the car’s original speed?

60 km/h

Let the car’s original speed be \(x\) km/h. The original time is \(\frac{240}{x}\) hours, and after increasing the speed to \(x+20\) km/h, the new time is \(\frac{240}{x+20}\) hours. Therefore, \(\frac{240}{x}-\frac{240}{x+20}=1\). On simplifying, \(x^2+20x-4800=0\), which factors as \((x-60)(x+80)=0\). Since speed must be positive, \(x=60\) km/h is the valid answer; \(-80\) km/h is rejected. Exam tip: In speed–time–distance problems, write the times for both situations first and then form their difference equation.

This is a Class 10 Mathematics question. Chapter: Quadratic Equations. Topic: Word Problems and Applications.