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Introduction to Rational Numbers

A crow flies ...

Question

A crow flies at a speed of 50 km/h for 3 hours and then at a speed of 40 km/h for further 2 hours. Find the average speed of the whole journey.

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Solution

Speed = $\frac{D i s t a n c e}{T i m e t a k e n}$
Distance = speed $\times$ time taken
1st part of its journey, the crow flies at a speed of 50km/h for 3 hours:
Distance covered by the crow = 50 x 3 = 150 km
2nd part of its journey, the crow flies at a speed of 40 km/h for 2 hours:
Distance covered by the crow = 40 x 2 = 80 km
Hence, total distance covered in 5 hours = 150 + 80 = 230 km
Average speed of the whole journey = $\frac{T o t a l d i s t a n c e}{T o t a l t i m e}$
= $\frac{230}{5}$ = 46 km/h

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