It’s just a double application of the two-event formula, first thinking of as a single event:

Answer from Brian M. Scott on Stack Exchange
🌐
Unacademy
unacademy.com › cbse class 11 › cbse class 11 study materials › mathematics › intersection of sets
set operations, the intersection of sets, the difference of sets
February 16, 2022 - It is represented by the symbol “∩”. For any two sets P and Q, the intersection, P ∩ Q, also read as P intersection Q, lists all the common elements of P and Q. For example, if a set P = {2, 4, 6, 8, 10, 12} and set Q = {3, 6, 9, 12}, then P ∩ Q = {6, 12}.
🌐
Filo
askfilo.com › mathematics exemplar › triangles › in figure, if a b | d c and a c, p q intersect each other at t
[Solved] In figure, if A B \| D C and A C, P Q intersect each other at th..
Solution For In figure, if A B \| D C and A C, P Q intersect each other at the point 0 . Prove that O A \cdot C Q=O C \cdot A P. - Mathematics Exempla
Published   March 23, 2023
🌐
Toppr
toppr.com › ask › question › given-p-a-b-c-d-e-q-a-e-i-o-u-and-r
Given P = a, b, c, d, e, Q = a, e, i, o, u and R = a, c, e, g. Verify the associative property of set intersection.
December 26, 2019 - Click here👆to get an answer to your question ✍️ Given P = a, b, c, d, e, Q = a, e, i, o, u and R = a, c, e, g. Verify the associative property of set intersection.
🌐
Probability Course
probabilitycourse.com › chapter1 › 1_4_0_conditional_probability.php
Conditional Probability | Formulas | Calculation | Chain Rule | Prior Probability
Let us write the formula for conditional probability in the following format $$\hspace{100pt} P(A \cap B)=P(A)P(B|A)=P(B)P(A|B) \hspace{100pt} (1.5)$$ This format is particularly useful in situations when we know the conditional probability, but we are interested in the probability of the intersection.
🌐
Wikipedia
en.wikipedia.org › wiki › Intersection_(set_theory)
Intersection (set theory) - Wikipedia
November 24, 2025 - The most general notion is the intersection of an arbitrary nonempty collection of sets. If ... {\displaystyle \left(x\in \bigcap _{A\in M}A\right)\Leftrightarrow \left(\forall A\in M,\ x\in A\right).} The notation for this last concept can vary considerably. Set theorists will sometimes write " ... {\displaystyle I} is the set of natural numbers, notation analogous to that of an infinite product may be seen:
🌐
Wikipedia
en.wikipedia.org › wiki › Conditional_probability
Conditional probability - Wikipedia
3 days ago - A is assumed to be the set of all possible outcomes of an experiment or random trial that has a restricted or reduced sample space. The conditional probability can be found by the quotient of the probability of the joint intersection of events A and B, that is,
🌐
Cuemath
cuemath.com › geometry › intersect
Intersect - Cuemath
They have a common point called the point of intersection. In the figure shown below, we can see line P and line Q are intersecting at point O.
Find elsewhere
🌐
Vedantu
vedantu.com › question-answer › if-p-and-q-are-the-points-of-intersection-of-the-class-12-maths-cbse-5f673778eee2a36606bbc14e
If P and Q are the points of intersection of the circles class 12 maths CBSE
The correct option is B. Note: The radical axis is the common chord of the two circles which passes through their intersection points. This is why, while finding the circle passing through the two intersecting points, we took the radical axis into consideration.
Top answer
1 of 2
1
P∩Q = P - Q P∩Q implies elements that are both in set P and Q.           P∩Q={x:x∈P and x∈Q}Explanation:Convergence of sets is the arrangement of components which are normal to both the given sets. In set hypothesis, for any two sets An and B, the convergence is characterized as the arrangement of the multitude of components in set A that are likewise present in set B. We utilize the image '∩' that signifies 'crossing point of'. For instance, let us address the understudies who like frozen yogurts for dessert, Brandon, Sophie, Luke, and Jess. This is set A. The understudies who like brownies for pastry are Ron, Sophie, Mia, and Luke. This is set B. The understudies who like both frozen yogurts and brownies are Sophie and Luke. This is addressed as A ∩ B.Properties of Intersection of SetsCrossing point of sets have properties like the properties of numbers. The properties of crossing point of sets incorporate the commutative regulation, cooperative regulation, law of invalid set and general set, and the idempotent regulation. The properties of the convergence of sets.Commutative LawA ∩ B = B ∩ AAssociative Law(A ∩ B) ∩ C = A ∩ (B ∩ C)Law of ϕ and U ϕ ∩ A = ϕ , U ∩ A= AIdempotent Law (A ∩ (B ∪ C) = (A ∩ B) ∪ (A ∩ C)(A ∪ (B ∩ C) = (A ∪ B) ∩ (A ∪ C)To know more about sets visit the links given below:https://brainly.in/question/3282530https://brainly.in/question/3978598
2 of 2
11
Answer The union of two sets P and Q is represented by P ∪ Q. This is the set of all different elements that are included in P or Q. The symbol used to represent the union of set is ∪. The intersection of two set P and Q is represented by P ∩ Q.Union of Set: Intersection of SetIt rejects the identical values from the set: It is an associative operation which includes.
🌐
Cuemath
cuemath.com › algebra › intersection-of-sets
Intersection of Sets - Formula, Examples | A intersection B
The intersection of two given sets is the set that contains all the common elements of both sets. The symbol for the intersection of sets is " ∩''. Learn more about the intersection of sets with concepts, definitions, properties, and examples.
🌐
Vedantu
vedantu.com › question-answer › if-a-a-b-c-d-b-p-q-r-s-then-which-of-the-class-11-maths-cbse-5f6b244f94c68525d4969acf
If A = (a, b, c, d), B = (p, q, r, s) then which of the following are relation from a to b$a){{R}_{1}}=\\left\\{ \\left( a,p \\right),\\left( b,r \\right),\\left( c,s \\right) \\right\\}$$b){{R}_{2}}=\\left\\{ \\left( q,b \\right),\\left( c,s \\right),\\left( d,r \\right) \\right\\}$$c){{R}_{3}}=\\left\\{ \\left( a,p \\right),\\left( a,q \\right),\\left( d,p \\right),\\left( c,r \\right),\\left( b,r \\right) \\right\\}$$d){{R}_{4}}=\\left\\{ \\left( a,p \\right),\\left( a,q \\right),\\left( b,s \\right),\\l
Complete step-by-step answer: Now consider option $a){{R}_{1}}=\left\{ \left( a,p \right),\left( b,r \right),\left( c,s \right) \right\}$ Here the relation is ${{R}_{1}}$ now let us consider all three elements In $\left( a,p \right)$ we have $a\in A,p\in B$ In $\left( b,r \right)$ we have $b\in A,p\in B$ In $\left( c,s \right)$ we have $c\in A,q\in B$ Hence all the elements are of the form $(x,y):x\in A,y\in B$ hence we have ${{R}_{1}}$ is a relation Now consider option $b){{R}_{2}}=\left\{ \left( q,b \right),\left( c,s \right),\left( d,r \right) \right\}$ Here if we consider the first element itself $(q,b)$ is such that \[q\in B,b\in A\] this element is not in the form of $(x,y):x\in A,y\in B$ .
Top answer
1 of 4
52

Any probability result that is true for unconditional probability remains true if everything is conditioned on some event.

You know that by definition, $$P(A\mid B) = \frac{P(A\cap B)}{P(B)}\tag{1}$$ and so if we condition everything on $C$ having occurred, we get that $$P(A\mid (B \cap C)) = \frac{P((A\cap B)\mid C)}{P(B\mid C)}\tag{2}$$ which is the result that puzzles and surprises you; you think it should be $$P(A\mid (B \cap C)) = \frac{P(A\cap B \cap C)}{P(B\cap C)}.$$

So, let's start by setting $D = B\cap C$ write $P(A\mid (B \cap C)) = P(A\mid D)$ as in $(1)$ to get \begin{align} P(A\mid (B \cap C)) &= P(A\mid D)\\ &= \frac{P(A\cap D)}{P(D)}\\ &= \frac{P(A\cap (B \cap C))}{P(B\cap C)}\\ &= \frac{P(A\cap B \cap C)}{P(B\cap C)}\tag{3}\end{align} which is what you think the result should be. But observe that if you multiply and divide the right side of $(3)$ by $P(C))$, you can get \begin{align} P(A\mid (B \cap C)) &= \frac{P(A\cap B \cap C)}{P(B\cap C)}\times \frac{P(C)}{P(C)}\\ &= \dfrac{\dfrac{P(A\cap B \cap C)}{P(C)}}{\dfrac{P(B\cap C)}{P(C)}}\\ &= \dfrac{P(A\cap B \mid C)}{P(B\mid C)} \end{align} which is just $(2)$. In short, the intuition about $(2)$ is that it is just $(3)$ (which you agree with) re-written in terms of conditional probabilities conditioned on the same event $C$.

2 of 4
27

Just draw the Venn diagram. We then have $$\Pr[A \cap B \mid C] = \frac{\text{"1"}}{\text{"C"}}, \quad \Pr[B \mid C] = \frac{\text{"1"} + \text{"2"}}{\text{"C"}}, \quad \Pr[A \mid B \cap C] = \frac{\text{"1"}}{\text{"1"} + \text{"2"}},$$ and the relationship follows by dividing the first expression by the second.

🌐
Probability Course
probabilitycourse.com › chapter1 › 1_4_1_independence.php
Independence | Conditional Independence
Thus, if two events $A$ and $B$ are independent and $P(B)\neq 0$, then $P(A|B)=P(A)$. To summarize, we can say "independence means we can multiply the probabilities of events to obtain the probability of their intersection", or equivalently, "independence means that conditional probability of one event given another is the same as the original (prior) probability". Sometimes the independence of two events is quite clear because the two events seem not to have any physical interaction with each other (such as the two events discussed above).
Top answer
1 of 1
2
SET OPERATIONSAnswer: P∩Q∩R is {c, d, e} (D).FURTHER EXPLANATION:What are set operations?The set operations are performed on two or more sets to obtain a combination of elements as per the operation performed on them.There are four main kinds of set operations which are as follows.Union of setsIntersection of setsComplement a setDifference between sets/Relative ComplementUnion of Set1) The union of two sets A and B can be given by:A ∪ B = {x | x ∈ A or x ∈ B}This operation on the elements of set A and B can be represented using a Venn diagram with two circles.2) Intersection of SetIf two sets A and B are given, which consist of elements common to both A and B. Then the intersection of A and B is the subset of universal set U, which can be given by:A ∩ B = {x : x ∈ A and x ∈ B}The intersection of 3 sets If A, B, and C are three sets, then all of the elements that are shared by A, B, and C are contained in the set formed by the intersection of these three sets. This can be shown as A∩B∩C. Following is a list of some properties of the intersection operation:Commutative law: A ∩ B = B ∩ AAssociative law: (A ∩ B) ∩ C = A ∩ (B ∩ C)Idempotent law: A ∩ A = ADistributive law: A ∩ (B U C) = (A ∩ B) U (A ∩ C)3) Complement of SetThe Complement of a Set A is the set of all the elements which are the elements of the Universal set but not the elements of A. It is represented by the symbol A' or [tex]A^C[/tex].4)Difference between sets/Relative ComplementThe Relative Complement of set A with respect to set B is the set of all the elements present in B but not in A. It is also called the difference between two sets A and B representing “A-B”. Here we are talking about the relation of complements of sets A and B only not related to universal set.A - B = {x: x∈ A and x∉ B} = A∩B′B - A = {x: x∈ B and x ∉ A} =B∩A′Example 1:If A = {1, 2, 3, 4, 5}, B = {2, 4, 6}, U = {1, 2, 3, 4, 5, 6, 7, 8}.Here are the following operations on sets and the solutions.A ∪ B = {1, 2, 3, 4, 5, 6}A ∩ B = {2, 4}A′ = {6, 7, 8}A - B = {1, 3, 5}Now, we can complete the given problem with the previous explanation.Be Discovered:P = (a, b, c, d, e}Q = {a. c. e, d. t}R = {t, d, c, b, e}Question: P∩Q∩RSolution:Find P∩QP∩Q = {a, c, d, e} With Associative law: (P ∩ Q) ∩ R = P ∩ (Q ∩ R)P∩Q∩R = (P ∩ Q) ∩ RThen, find {a, c, d, e} ∩ RP∩Q∩R = {a, c, d, e} ∩ {t, d, c, b, e}P∩Q∩R = {c, d, e}Therefore, P∩Q∩R is {c, d, e} (D). Learn more about set operations and the Venn diagram here:https://brainly.ph/question/18351065#SPJ2