Jenna invest R20000 into saving account.the interest paid in the account is 10%pa compounded mounthly.calculate how (in years) it will take for the saving to reach R80000.

Answer 1

80000/20000 = 4
so you want the time to grow by a factor of 4:

(1+.10/12)^(12t) = 4
Now just solve for t.