A cyclist travels 25 km at 5 km/h and then a further 80 km at 40 km/h. What is his average speed of the journey?

25 km/h

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5 km/h

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20 km/h

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15 km/h

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Solution

The correct option is D
15 km/h

Time taken = $\frac{D i s t a n c e}{S p e e d}$

Ist leg of the journey: Distance = 25 km, Speed = 5 km/h

Time taken to cover the 1st leg of the journey = $\frac{25}{5}$ = 5 hours

2nd leg of the journey: Distance = 80 km, speed = 40 km/h

Time taken to cover the 2nd leg of the journey = $\frac{80}{40}$ = 2 hours

Time taken to cover the entire journey = 5 + 2 = 7 hours

Average speed for the whole journey = $\frac{T o t a l d i s t a n c e t r a v e l l e d}{T o t a l t i m e t a k e n}$

= $\frac{25 + 80}{7}$ = $\frac{105}{7}$ = 15 km/h

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