Question

A cyclist travels from City A to City B at an average speed of 20 km/h and takes 4 hours. If they want to complete the same journey in 2.5 hours, by what amount (in km/h) should they increase their average speed?

• A. 12 km/h
• B. 10 km/h
• C. 15 km/h
• D. 8 km/h

Answer 1

Answer:

A. 12 km/h

Distance between City A and City B:

$\text{Distance} = \text{Speed} \times \text{Time}$
$= 20 \times 4 = 80 \text{ km}$

To cover 80 km in 2.5 hours, the required speed is:

$\text{Required Speed} = \frac{80}{2.5} = 32 \text{ km/h}$

Increase in speed:

$32 - 20 = 12 \text{ km/h}$

Answer

$\boxed{12 \text{ km/h}}$

The cyclist must increase their average speed by 12 km/h.