Question 877233
i=Prt where i is the interest collected, P is the starting principal, r is the interest rate, and t is the time.  Since the time is given in years, the interest is considered as yearly interest rate.<P>
Call the starting Principal x, since it is unknown.  Add the principal, x, to the accumulated interest, to have three times the original amount.  x is the original amount, 3x is three times the original amount, so 2x interest is needed.<P>
2x = x*20*r<P>
2x=20xr
2x/20x=r=1/10 = .1 = 10% interest.