Yields on short-term bonds tend to be more volatile than yields on long-term bonds. Suppose that you have estimated that the yield on 20-year bonds changes by 10 basis points for every 21-basis-point move in the yield on 5-year bonds. You hold a $2.1 million portfolio of 5-year maturity bonds with modified duration 4 years and desire to hedge your interest rate exposure with T-bond futures, which currently have modified duration 9 years and sell at F₀ = $70. How many futures contracts should you sell?

Answer is not 13 future contracts.