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Let the equation of population growth is N(t) = No * 2^(t/a)
292000= 146000* 2^(18/a) ; or 2= 2^(18/a) ; solving we get a = 18
hence we can write ; 500000=146000* (2)^(t/18)
or 3.42 = 2^(t/18) ; soling we get t = 31.93 years
hence Answer : 32 years
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