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प्रश्न
An aeroplane flies, along the four sides of a square at speeds of 100, 200, 300 and 400 kilometres per hour respectively. What is the average speed of the plane in its flight around the square?
उत्तर
Harmonic mean would he suitable. The harmonic mean of n observations is HM = `"n"/(sum 1/"x")`
Here n = 4
∴ HM = `4/(1/100 + 1/20 + 1/300 + 1/400)`
= `4/(((12 + 6 + 4 + 3)/1200))`
= `4/((25/1200))`
= `(4 xx 1200)/25`
= 4 × 48
= 192 km/hr
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