(Hint: See Example 41]
4. A man having to drive 90 km wishes to achieve an average speed of 30 km per hour. For the
first half of the journey, he averages only 20 km per hour. What must be his average speed
for the second half of the journey if his overall average speed is to be 30 km per hour?
[Ans. X 2= 60 mph)
Answers
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Answer:
ans) X 2 = 60 mph
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Given,
Distance covered = 90 km.
Half distance covered with speed = 30 km/hr
Remain half with a speed = v
Average speed = 48km/hr
To Find,
Value of speed (v)
Solution,
Average speed =
Let, t₁ = initial time taken.
t₂ = final time taken.
Total time =
=
Total distance = 90km
So according to question,
30 =
v + 40 = 100
v = 60 km/hr.
Hence, the average speed of the second half of the journey is 60km/hr.
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