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1. The speed of the train going from Nagpur to Allahabad is 100 km/h while when coming back from Allahabad to Nagpur, its speed is 150 km/h. find the average speed during whole journey.

A. 125 km/hr

B. 75 km/hr

C. 135 km/hr

D. 120 km/hr

Solution:

\begin{aligned} Average speed, \\ = \frac{2 \times x \times y}{x + y} \\ = \frac{2 \times 100 \times 150}{100 + 150} \\ = \frac{200 \times 150}{250} \\ = 120 km/hr \end{aligned}

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