<prompt> A couple has 4 children, all unvaccinated for Measles. A child got Measles on 5 August 2015. Two other children developed Measles by 15 August 2015. Secondary attack rate is:0336675  <response>: In the given question, One primary case given rise to two secondary cases Total susceptible 3 4 children minus primary case SAR No. of secondary cases Total susceptibles X 100 So, SAR 23 X 100 66.6 