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Question
In 1975, the consumption of water for human use was about 3850 cu.km/year. It increased to about 6000 cu.km/year in the year 2000. Find the per cent increase in the consumption of water from 1975 to 2000. Also, find the annual per cent increase in consumption (assuming water consumption increases uniformly).
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Solution
The consumption of water for human in 1975 = 3850 cu km/yr
The consumption of water for human in 2000 = 6000 cu km/yr
Increase in consumption of water in 1975 to 2000 = 6000 – 3850 = 2150 cu km/yr
In percentage = `2150/3850 xx 100 = 55.84%`
In 25 yr total increase in water consumption = 2150 cu km/yr
∴ Annually, i.e. per year water consumption =`2150/25` = 86 cu km/yr ...[∵ 2000 – 1975 = 25 yr]
∴ In percentage = `86/3850 xx 100`
= `8600/3850`
= 2.23%
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