SOLUTION:
Total=A+B+C− {Sum of Exactly 2 groups members} −2∗A∩B∩C+ Neither
Given:
Total = 600 and as a percentage it is 100%
Neither = 0 (As all the students have chosen at least one of these three subjects).
Math (M) = 35%
Science(S) = 40%
History (H) = 50%
Percent chose exactly 2 of these subjects = 18 %
Let M∩H∩S = x
Using the formulae stated above:
100 = 35 + 40 + 50 – 18 -2x + 0
=>100 = 107 - 2x
=> x =7/2 % = 7/200 * 600 = 21 (OPTION D)