n(A) = 21, n(B) = 27, n(c) = 34,
n(A ∩ B) = 15,
n(B ∩ C) = 14, n(C ∩ A) = 13
n(A ∪ B ∪ C) = 100 - 5 = 95
Using = n(A ∪ B ∪ C) = n(A) + n(B) + n(c) - n(A ∩ B) -n(B ∩ C) - n(C ∩ A) + n(A ∩ BAC)
95 = 21 + 27 + 34 - 15 - 14 - 13 + n(A ∩ B ∩ C)
95 = 82 - 42 + n(A ∩ B ∩ C)
95 = 40 + n(A ∩ B ∩ C)
n(A ∩ B ∩ C)= 45% students