This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Measurement of Mortality and Morbidity, Subject name: Social & Preventive Medicine
Out of 10 relatives exposed to a primary case, of measles, 6 developed measles. Secondary attack rate of measles- 
Select and explain. 
A. 10-Apr, B. 10-Jun, C. 6-Apr, D. 4-Jun
B: 10-Jun
Answer: B: 10-Jun 
Explanation: Ans. is 'b' i.e., 6/10 Secondary attack rate (SAR)o SAR is defined as "the number ofexposed persons developing the disease within the range of incubation period, following exposure to primary caseSAR=No of exposed persons developing disease withinthe range of the incubation period-----------------------Total number of exposed/susceptible contactx 100 SAR =610x 100