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Question
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?
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Solution
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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