Question
At the rate of any compound interest rate, it gets
tripled in 4 years, in how many years it will become 729 times its own?Solution
Let the principal be Rs. x, then Amount = 3x As we know, A = P (1+r/100)t 3x = x (1 + r/100)4 (1+r/100) = 4√3       ...i) Again, A = 729x, P = x 729x = x (1 + r/100)t (1+r/100) = t√729    ...ii) From equation (i) 4 √3= t√729 31/4 = 36/t Compare on powers. 1/4 = 6/t t = 24 years Smart Approach-       In 4th year = 3 times.  After T years =729=36 T=4×6=24 years.
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