\"T2 rule\

"72 rule" , formulated as T is a quick way to estimate the time T for a portfolio to double its initial amount given a fixed level of compounded yield r. For example, if the yearly interest rate is it will take approximately 10 years for a saving account to double its balance. (a) Suppose Sl was invested in 60 years ago at 3.6% interest compounded yearly, approximate how much would that investment worth today? (b) The equation (1 + 2 implies the time required to double the initial invested amount is T 0.69 When r is small, recall the relation In(l + r) r r2/2 = r(l r/2) in calculus. Show that when