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1.
a motor -cycle covers 40 Km with a speed of 20 km /hr. Find the speed of the motor -cycle for the next 40 km journey so that the average speed of the whole journey will be 30 km / hr.
- A. 70.0km /hr
- B. 70.0km /hr
- C. 70.0km /hr
- D. 70.0km /hr
Answer: Option C
Explanation:
Let the desired speed be x km/hr
ATQ,
40/20 + 40/x = 80/30
Or, 1/20 + 1/x = 2/30
Or, 1/x = 1/15 - 1/20
Or, 1/x = (4 - 3)/60
Or, x = 60
So, the desired speed is 60 km/hr
ATQ,
40/20 + 40/x = 80/30
Or, 1/20 + 1/x = 2/30
Or, 1/x = 1/15 - 1/20
Or, 1/x = (4 - 3)/60
Or, x = 60
So, the desired speed is 60 km/hr
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