Average age of seven persons sitting in a row facing east is 28 years. If the average age of the first three persons is 21 years and the average age of the last three persons is 34 years, then find the age of the person sitting in the middle of the row ?

Total age seven persons = (28 * 7)years

Total age of the first three persons and the last three persons are (21 * 3) years and (34 * 3) years respectively.
Age of the person sitting in the middle of the row = 28 * 7 – 21 * 3 – 34 * 3 = 196 – 63 – 102 = 31 years