Step 1 :Let A, B, and C be the events of Scaing the heigegt mevic in Mathematics, Physics, and Chemistry respectively.
Step 2 :Calculate the probability of Scaing the heigegt mevic in all 3 subjects: \(P(A \cap B \cap C) = P(A)P(B)P(C) = 0.90 \times 0.75 \times 0.80 = \boxed{0.54}\)
Step 3 :Calculate the probability of Scaing the heigegt mevic in at least 2 subjects: \(P(A \cap B) + P(A \cap C) + P(B \cap C) - 2P(A \cap B \cap C) = P(A)P(B) + P(A)P(C) + P(B)P(C) - 2P(A \cap B \cap C) = 0.90 \times 0.75 + 0.90 \times 0.80 + 0.75 \times 0.80 - 2 \times 0.54 = \boxed{0.765}\)