A team of medical students doing their internship have to assist during surgeries at a city hospital. The probabilities of surgeries rated as very complex, complex, routine, simple or very simple are respectively, 0.15, 0.20, 0.31, 0.26, .08. Find the probabilities that a particular surgery will be rated
(a) complex or very complex;
(b) neither very complex nor very simple;
(c) routine or complex
(d) routine or simple
Given:
P (E1) = 0.15
P (E2) = 0.20
P (E3) = 0.31
P (E4) = 0.26
P (E5) = 0.08
Let us consider that –
E1 → Event that surgeries are rated as very complex
E2 → Event that surgeries are rated as complex
E3 → Event that surgeries are rated as routine
E4 → Event that surgeries are rated as simple
E5 → Event that surgeries are rated as very simple
= P (E1 U E2)
Now, by the general rule –
P (A U B) = P(A) + P(B) – P(A ∩ B)
We have,
P (E1 U E2) = P(E1) + P(E2) – P(E1 ∩ E2)
= 0.15 + 0.2 – 0
= 0.35
= 1 - P (E1 ∩ E5) ….. (by complement rule)
= 1 – [P (E1) + P (E5) – P (E1 ∩ E5) … (general addn rule)
= 1 – [0.15 + 0.08 – 0]
= 1 – 0.23
= 0.77
= P (E3) + P (E2) - P (E3 ∩ E2) …… (by general addition rule)
= 0.31 + 0.2 – 0
= 0.51
= P (E3) + P (E4) - P (E3 ∩ E4) …… (by general addition rule)
= 0.31 + 0.26 - 0
= 0.57