A train travels 40 km at a uniform speed of $30 k m h^{- 1}$ . Its average speed for the whole journey after travelling another 40 km is $45 k m h^{- 1}$ . Its speed in the second half of the journey is ____.

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A car travels from A to B at a, speed of 20kmh−1 and returns at a speed of 30kmh−1. The average speed of the car for the whole journey is:

The correct option is B 24kmh−1Let distance from A to B be xTime for travel from A to B= x/20Time for travel from B to A= x/30Hence,speed for total distance 2x is: 2xx30+x20=2x×605x=24 km\hr

A car travels from A to B at a, speed of $20 k m h^{- 1}$ and returns at a speed of $30 k m h^{- 1}$ . The average speed of the car for the whole journey is:

The correct option is B $24 k m h^{- 1}$
Let distance from A to B be x
Time for travel from A to B= x/20
Time for travel from B to A= x/30
Hence,speed for total distance 2x is: $\frac{2 x}{\frac{x}{30} + \frac{x}{20}} = \frac{2 x \times 60}{5 x}$ =24 km\hr