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  • Brainly User
2014-09-10T16:25:02+05:30
Let sum invested = P for t years.
A sum will be doubled if interest = principal = P. Amount = P+P = 2p.
Amount 2P = Px[1 + (20/100)]^t  
 Hence [1 + (20/100)]^t = 2 
or (1.21)^t = 2
LHS is greater than two when t = 4 
Hence sum will be more than doubled if it is invested for 4 years.
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