When the average price of an item increases from $p_1$ to $p_2$ over a period of $n$ years, the annual rate of inflation $r$ (in decimal form) is given by $r=\left(\frac{p_2}{p_1}\right)^{1/ n}-1$ . The average price of one pound of rice increased from $0.08 in 1913 to $0.72 in 2013. What was the annual rate of inflation $r$ ? Write your answer in decimal form to the nearest thousandth.