An investor has a portfolio consisting of 20,000 worth of a 2 year bond with a modified duration of 1.92, 35,000 worth a 3 year bond with a modified duration of a 2.84 and a 45,000 worth of a 5 year bond with a modified duration of a 4.79. Find the modified duration of the whole portfolio

a. 3.49 b. 3.53 c. 3.57 d. 3.61 e. 3.65

Please, no excel spreadsheets