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A person takes a certain time to reach office from home with usual speed and while returning from the office towards home, he decreases his speed by 20% from his usual speed and takes 6 minutes more, then what is his usual speed if the distance between home and office is 20 km?

A person takes a certain time to reach office from home with usual speed and while returning from the office towards home, he decreases his speed by 20% from his usual speed and takes 6 minutes more, then what is his usual speed if the distance between home and office is 20 km? Correct Answer 50 km/h

Given:

Person decreased his speed while returning by 20%

Time taken by the person = 6 minutes + usual speed 

Distance between home and office = 20 km 

Formula Used:

Distance = Speed × Time 

Calculation:

Suppose original speed = 5x and decreases speed = 80% of 5x = 4x

According to the question :

⇒ (20/4x) – (20/5x) = (6/60)

⇒ (5/x) – (4/x) = 0.1

⇒ 1/x = 0.1

⇒ x = 10

∴ Usual sped = 5x = 50 km/h

 

Shortcut Trick 

Ratio of speed = 5 : 4

Ratio of time taken = (1/5) : (1/4) = 4 : 5

Difference = 1 = 6 min

Usual time taken = 4 = 6 × 4 = 24 minutes

Usual speed = (20/24) × 60 = 50 km/h

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