rakeshmeher wrote:A nation's population triples every 100 years. If the population was 100,000 in the year 1200, in what year was the population 72,900,000?
Any short method !!!!!!!!!!!!!!
When an amount keeps being multiplied by the same value over and over, use
the formula for exponential change:
Final Amount = Original Amount * Multiplier^(number of changes)
In the problem above:
The final amount is 72,900,000
The original amount is 100,000
The multiplier is 3 (because the population keeps tripling)
What we don't know is the number of changes: the number of times the population will have to triple in order to reach 72,900,000. We need to solve for this value.
So plugging our known values into the formula, we get:
72,900,000 = 100,000 * 3^x
729 = 3^x
Since 3^6 = 729, x = 6.
The population has to triple 6 times. Since it triples every 100 years, 6 * 100 = 600 years will be needed for the population to reach 72,900,000.
Since the starting year is 1200, 1200+600= 1800.
Last edited by
GMATGuruNY on Tue Jun 29, 2010 7:07 am, edited 1 time in total.
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