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Two-thirds of a certain distance was covered at the speed of 45 km/h, one-fourth at the speed of 60 km/h and the rest at the speed of 75 km/h. Find the average speed per hour for the whole journey. (correct to 2 decimal places)
Answer & Solution
Correct Answer:
Option
D
$$\eqalign{
& {\text{Let distance}} = 1200{\text{ km}} \cr
& {\text{Average speed}} = \frac{{1200}}{{\frac{{800}}{{45}} + \frac{{300}}{{60}} + \frac{{100}}{{75}}}} \cr
& = \frac{{1200}}{{\frac{{160}}{9} + 5 + \frac{4}{3}}} \cr
& = \frac{{1200 \times 9}}{{217}} \cr
& = 49.77{\text{ km/h}} \cr} $$
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