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A car travels 20 miles at 30 mph, then 10 miles at 60 mph. What is the mean speed for the whole journey of 30 miles?
A. 36
B. 40
C. 42
D. 45
answer is 36 but I don’t understand. can you explain sirThe time taken for 20 miles will be 20/30 x 60 = 40 minutes
The time taken for the other 10 miles will be 10/60 x 60 = 10 minutesSo the total time for 30 miles will be 50 minutes (or 50/60 hours).
Therefore the average speed = 60/50 x 30 = 36 miles per hour.
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