$\"\"$

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The population function is $\"\"$ , where $\"\"$ (in billions of people) in year $\"\"$ .

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(a)

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when will the population of the world be $\"\"$ billion people.

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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Apply logarithm one to one property : if $\"\"$ ,then $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Therefore,the population of the world will be $\"\"$ billion people in $\"\"$ .

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$\"\"$

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(b)

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When will the population of the world be $\"\"$ billion people.

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Substitute $\"\"$ in $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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Apply logarithm one to one property : if $\"\"$ ,then $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Therefore,the population of the world will be $\"\"$ billion people in $\"\"$ .

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$\"\"$

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(a) The population of the world will be $\"\"$ billion people in $\"\"$ .

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(b) The population of the world will be $\"\"$ billion people in $\"\"$ .