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44. / took Malcom 3.5 hours to drive from city A to city B. on his way
back to city A, he increased his speed by 20 km per hour and it took him
3 hours. Find the average speed for the whole journey.
a)120.Okm/hr b) 129.2km/hr c) 125km/hr d)139km/hr
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Answers
Given : Malcom took 3.5 hours to drive from city A to city B.
on his way back to city A, he increased his speed by 20 km per hour and it took him 3 hours.
To Find : the average speed for the whole journey.
a)120.0km/hr b) 129.2km/hr c) 125km/hr d)139km/hr
Solution:
Let say Distance from A to B = 21D km
Malcom took 3.5 hours to drive from city A to city B.
So his speed = 21D/3.5 = 6D km/hr
on his way back to city A, he increased his speed by 20 km per hour and it
New speed = 6D + 20 km/hr
Time taken = 3 hr
Distance = (6D + 20) 3 = 18D + 60 km
18D + 60 = 21D
=> 3D = 60
=> D = 20
21D = 21(20) = 420 km
Total Distance = 420 + 420 = 840 km
Total Time taken = 3 + 3.5 = 6.5 hrs
Average Speed = 840/6.5
= 129.23 km/hr
= 129.2km/hr
average speed for the whole journey. 129.2km/hr
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