Q - A population of 750 healthy females was followed for the development of heart disease for 25 years. 75 of these females developed heart at 7 years, then another 50 developed it at 15 years, and 10 died from other causes at the end of observation period. Another 55 females were lost to follow up at 3 years. The remainder were followed for the entire period. Calculate the Incidence density/incidence rate of heart disease in this population?