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Motorcyclist moves at an average speed of 30 kmph, reaches its destination on time. When its average speed becomes 18 kmph, then it reaches its destination 12 minutes late. Find the length of journey.


1. 9 km 
2. 10 km 
3. 12 km 
4. 13 km 
5. None of these 

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Correct Answer - Option 1 : 9 km 

Given:

When speed is 30 kmph reaches on time

When speed is 18kmph reaches 12 min early

Formula:

Time = distance/speed

Calculation:

Let the distance be 'x' km

Therefore time taken to cover 'x' km at 30 kmph = x/30​ hr

Time taken to cover 'x 'km at 18 kmph = x/18​ hr

But it is given that the difference between two timings 

⇒ 0 + 12 = 12 min = 12/60​ hr = 1/5

⇒ x/18 ​– x/30 ​= 1/5

⇒ (30x − 18x)​/(18 × 30) = 1/5​

⇒ 12x/​(18 × 30) = 1/5

⇒ x = (1 × 18 × 30)/(12 × 5)

⇒x = 9 km 

Length of journey is 9km.

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