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Hello!

I can understand the following numeral expressions. Especially the last sentence. Give me some easy example for understanding, if possible.

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Population growth is more than a simple addition of people. If it were just that, the addition of 20 people a year to a population of 1,000 would result in that population's being dubled in 50 years; but because the added people beget more people, the doubling time is actually much less. Hence, it took the whole of human history and prehistory for the world's population to reach one billion people, which was achieved in 1850. By 1950, world population had reached almost 2.5 billion, representing an annual growth rate of about 0.8 percent. Between 1950 and 1960, the rate of growth had climbed to 1.8 percent - doubling time 39 years.

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My question is

(1) following the above formular, what is the population 1960?

(2) what does that 'doubling time 39 years' mean?

Thank you!!
Comments  
1) I don't know. Take 2.5 billion and apply a compound rate of 1.8 percent for ten years. I'm not good at these formulas.

2) The length of time it will take for the population to double.
I think the answer for (1) is not important. That is a math question. Help me a little more, please.

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1950, world population had reached almost 2.5 billion, representing an annual growth rate of about 0.8 percent. Between 1950 and 1960, the rate of growth had climbed to 1.8 percent - doubling time 39 years.

doubling time 39 years = The length of time it will take for the population to double.
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Do you mean that the time to sum up to 5 billion will take 39 years? That is, the population will be 5 billion by 1999, right? Thank you so much!!
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That's certainly what is implied. However 1999 came and went. Did the world population reach 5 billion? I don't know.

As for #1, you asked it.
Thank you.

For #1, I should have said that if you know the answer for #2, it is not important to answer the #1. If you felt uneasy or insulted, sorry.

If you are not busy, I want to ask once more. How do you translate 'doubling time 39 years' that way?

I mean, you Eng speakers think the phrase 'the doubling time will be 39 years.'

But, I guessed it would mean 'doubling + time(39 years)'.

I mean, if there were 'the' , I might get the idea. Since, (the doubling time / 39 years) is easy to catch. But without 'the', double seems like a verb, and made me think ( doubling (present participle) / time(object) 39 years ( apposition of time) )

What do you think about my thinking? I am asking if there were 'the' in the sentence, would it be better? Or, is the sentence itself a good one without 'the'?
I would translate "doubling time" as "the time it takes for the population to double." I find that more clear than the original, actually.
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Thank you!!