Probability proof. Check my answer?
$begingroup$
Let $A$ and $B$ be events defined on a sample space $Omega$. Prove that
$$textbf{P}(A cap B) geq 1 - textbf{P}(A^{c})- textbf{P}(B^{c}) $$
Answer:
begin{align*}
textbf{P}(Acap B) & = textbf{P}(A)textbf{P}(B) \
& = (1 - textbf{P}(A^{c}))(1 - textbf{P}(B^{c})) \
& = 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) + textbf{P}(A^{c})textbf{P}(B^{c}) geq 1 - textbf{P}(A^{c}) - textbf{P}(B^{c})
end{align*}
probability proof-verification
$endgroup$
add a comment |
$begingroup$
Let $A$ and $B$ be events defined on a sample space $Omega$. Prove that
$$textbf{P}(A cap B) geq 1 - textbf{P}(A^{c})- textbf{P}(B^{c}) $$
Answer:
begin{align*}
textbf{P}(Acap B) & = textbf{P}(A)textbf{P}(B) \
& = (1 - textbf{P}(A^{c}))(1 - textbf{P}(B^{c})) \
& = 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) + textbf{P}(A^{c})textbf{P}(B^{c}) geq 1 - textbf{P}(A^{c}) - textbf{P}(B^{c})
end{align*}
probability proof-verification
$endgroup$
2
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12
add a comment |
$begingroup$
Let $A$ and $B$ be events defined on a sample space $Omega$. Prove that
$$textbf{P}(A cap B) geq 1 - textbf{P}(A^{c})- textbf{P}(B^{c}) $$
Answer:
begin{align*}
textbf{P}(Acap B) & = textbf{P}(A)textbf{P}(B) \
& = (1 - textbf{P}(A^{c}))(1 - textbf{P}(B^{c})) \
& = 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) + textbf{P}(A^{c})textbf{P}(B^{c}) geq 1 - textbf{P}(A^{c}) - textbf{P}(B^{c})
end{align*}
probability proof-verification
$endgroup$
Let $A$ and $B$ be events defined on a sample space $Omega$. Prove that
$$textbf{P}(A cap B) geq 1 - textbf{P}(A^{c})- textbf{P}(B^{c}) $$
Answer:
begin{align*}
textbf{P}(Acap B) & = textbf{P}(A)textbf{P}(B) \
& = (1 - textbf{P}(A^{c}))(1 - textbf{P}(B^{c})) \
& = 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) + textbf{P}(A^{c})textbf{P}(B^{c}) geq 1 - textbf{P}(A^{c}) - textbf{P}(B^{c})
end{align*}
probability proof-verification
probability proof-verification
edited Jan 13 at 22:50
user1337
46110
46110
asked Jan 13 at 20:57
oamyoamy
1
1
2
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12
add a comment |
2
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12
2
2
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
Notice that
begin{align*}
&textbf{P}(Acup B) leq 1 Leftrightarrow textbf{P}(A) + textbf{P}(B) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) + 1 - textbf{P}(B^{c}) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) leq textbf{P}(Acap B)
end{align*}
Where we have used the following properties
begin{cases}
textbf{P}(X) leq 1\\
textbf{P}(X) = 1 - textbf{P}(X^{c})\\
textbf{P}(Xcup Y) = textbf{P}(X) + textbf{P}(Y) - textbf{P}(Xcap Y)
end{cases}
Hope this helps.
$endgroup$
add a comment |
$begingroup$
Note that $P(S^c)=1-P(S)$ and $P(Acup B)le 1$ therefore$$P(A)+P(B)-P(Acap B)le 1\P(A)+P(B)-1le P(Acap B)\P(A)+P(B)-1-1+1le P(Acap B)\-P(A^c)-P(B^c)+1le P(Acap B)$$and finally by rearranging the terms $$P(Acap B)ge 1-P(A^c)-P(B^c)$$with the equality if and only if $$Acup B=S$$
$endgroup$
add a comment |
$begingroup$
You wrote:
$$ textbf{P}(Acap B) = textbf{P}(A)textbf{P}(B) $$
I claim this is wrong. Suppose that we are flipping a fair coin. Let $A$ be the event the
coin comes up heads. Let $B$ be the event the coin comes up heads. This give us:
begin{align*}
textbf{P}(A) &= frac{1}{2} \
textbf{P}(B) &= frac{1}{2} \
textbf{P}(Acap B) &= frac{1}{2} \
textbf{P}(A)textbf{P}(B) &= frac{1}{4} \
end{align*}
Hence their is a contradiction and your original statement is wrong.
I hope this helps.
Bob
$endgroup$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3072509%2fprobability-proof-check-my-answer%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
Notice that
begin{align*}
&textbf{P}(Acup B) leq 1 Leftrightarrow textbf{P}(A) + textbf{P}(B) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) + 1 - textbf{P}(B^{c}) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) leq textbf{P}(Acap B)
end{align*}
Where we have used the following properties
begin{cases}
textbf{P}(X) leq 1\\
textbf{P}(X) = 1 - textbf{P}(X^{c})\\
textbf{P}(Xcup Y) = textbf{P}(X) + textbf{P}(Y) - textbf{P}(Xcap Y)
end{cases}
Hope this helps.
$endgroup$
add a comment |
$begingroup$
Notice that
begin{align*}
&textbf{P}(Acup B) leq 1 Leftrightarrow textbf{P}(A) + textbf{P}(B) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) + 1 - textbf{P}(B^{c}) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) leq textbf{P}(Acap B)
end{align*}
Where we have used the following properties
begin{cases}
textbf{P}(X) leq 1\\
textbf{P}(X) = 1 - textbf{P}(X^{c})\\
textbf{P}(Xcup Y) = textbf{P}(X) + textbf{P}(Y) - textbf{P}(Xcap Y)
end{cases}
Hope this helps.
$endgroup$
add a comment |
$begingroup$
Notice that
begin{align*}
&textbf{P}(Acup B) leq 1 Leftrightarrow textbf{P}(A) + textbf{P}(B) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) + 1 - textbf{P}(B^{c}) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) leq textbf{P}(Acap B)
end{align*}
Where we have used the following properties
begin{cases}
textbf{P}(X) leq 1\\
textbf{P}(X) = 1 - textbf{P}(X^{c})\\
textbf{P}(Xcup Y) = textbf{P}(X) + textbf{P}(Y) - textbf{P}(Xcap Y)
end{cases}
Hope this helps.
$endgroup$
Notice that
begin{align*}
&textbf{P}(Acup B) leq 1 Leftrightarrow textbf{P}(A) + textbf{P}(B) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) + 1 - textbf{P}(B^{c}) - textbf{P}(Acap B) leq 1 Leftrightarrow\\
& 1 - textbf{P}(A^{c}) - textbf{P}(B^{c}) leq textbf{P}(Acap B)
end{align*}
Where we have used the following properties
begin{cases}
textbf{P}(X) leq 1\\
textbf{P}(X) = 1 - textbf{P}(X^{c})\\
textbf{P}(Xcup Y) = textbf{P}(X) + textbf{P}(Y) - textbf{P}(Xcap Y)
end{cases}
Hope this helps.
answered Jan 13 at 21:04
user1337user1337
46110
46110
add a comment |
add a comment |
$begingroup$
Note that $P(S^c)=1-P(S)$ and $P(Acup B)le 1$ therefore$$P(A)+P(B)-P(Acap B)le 1\P(A)+P(B)-1le P(Acap B)\P(A)+P(B)-1-1+1le P(Acap B)\-P(A^c)-P(B^c)+1le P(Acap B)$$and finally by rearranging the terms $$P(Acap B)ge 1-P(A^c)-P(B^c)$$with the equality if and only if $$Acup B=S$$
$endgroup$
add a comment |
$begingroup$
Note that $P(S^c)=1-P(S)$ and $P(Acup B)le 1$ therefore$$P(A)+P(B)-P(Acap B)le 1\P(A)+P(B)-1le P(Acap B)\P(A)+P(B)-1-1+1le P(Acap B)\-P(A^c)-P(B^c)+1le P(Acap B)$$and finally by rearranging the terms $$P(Acap B)ge 1-P(A^c)-P(B^c)$$with the equality if and only if $$Acup B=S$$
$endgroup$
add a comment |
$begingroup$
Note that $P(S^c)=1-P(S)$ and $P(Acup B)le 1$ therefore$$P(A)+P(B)-P(Acap B)le 1\P(A)+P(B)-1le P(Acap B)\P(A)+P(B)-1-1+1le P(Acap B)\-P(A^c)-P(B^c)+1le P(Acap B)$$and finally by rearranging the terms $$P(Acap B)ge 1-P(A^c)-P(B^c)$$with the equality if and only if $$Acup B=S$$
$endgroup$
Note that $P(S^c)=1-P(S)$ and $P(Acup B)le 1$ therefore$$P(A)+P(B)-P(Acap B)le 1\P(A)+P(B)-1le P(Acap B)\P(A)+P(B)-1-1+1le P(Acap B)\-P(A^c)-P(B^c)+1le P(Acap B)$$and finally by rearranging the terms $$P(Acap B)ge 1-P(A^c)-P(B^c)$$with the equality if and only if $$Acup B=S$$
answered Jan 13 at 21:41
Mostafa AyazMostafa Ayaz
17k31039
17k31039
add a comment |
add a comment |
$begingroup$
You wrote:
$$ textbf{P}(Acap B) = textbf{P}(A)textbf{P}(B) $$
I claim this is wrong. Suppose that we are flipping a fair coin. Let $A$ be the event the
coin comes up heads. Let $B$ be the event the coin comes up heads. This give us:
begin{align*}
textbf{P}(A) &= frac{1}{2} \
textbf{P}(B) &= frac{1}{2} \
textbf{P}(Acap B) &= frac{1}{2} \
textbf{P}(A)textbf{P}(B) &= frac{1}{4} \
end{align*}
Hence their is a contradiction and your original statement is wrong.
I hope this helps.
Bob
$endgroup$
add a comment |
$begingroup$
You wrote:
$$ textbf{P}(Acap B) = textbf{P}(A)textbf{P}(B) $$
I claim this is wrong. Suppose that we are flipping a fair coin. Let $A$ be the event the
coin comes up heads. Let $B$ be the event the coin comes up heads. This give us:
begin{align*}
textbf{P}(A) &= frac{1}{2} \
textbf{P}(B) &= frac{1}{2} \
textbf{P}(Acap B) &= frac{1}{2} \
textbf{P}(A)textbf{P}(B) &= frac{1}{4} \
end{align*}
Hence their is a contradiction and your original statement is wrong.
I hope this helps.
Bob
$endgroup$
add a comment |
$begingroup$
You wrote:
$$ textbf{P}(Acap B) = textbf{P}(A)textbf{P}(B) $$
I claim this is wrong. Suppose that we are flipping a fair coin. Let $A$ be the event the
coin comes up heads. Let $B$ be the event the coin comes up heads. This give us:
begin{align*}
textbf{P}(A) &= frac{1}{2} \
textbf{P}(B) &= frac{1}{2} \
textbf{P}(Acap B) &= frac{1}{2} \
textbf{P}(A)textbf{P}(B) &= frac{1}{4} \
end{align*}
Hence their is a contradiction and your original statement is wrong.
I hope this helps.
Bob
$endgroup$
You wrote:
$$ textbf{P}(Acap B) = textbf{P}(A)textbf{P}(B) $$
I claim this is wrong. Suppose that we are flipping a fair coin. Let $A$ be the event the
coin comes up heads. Let $B$ be the event the coin comes up heads. This give us:
begin{align*}
textbf{P}(A) &= frac{1}{2} \
textbf{P}(B) &= frac{1}{2} \
textbf{P}(Acap B) &= frac{1}{2} \
textbf{P}(A)textbf{P}(B) &= frac{1}{4} \
end{align*}
Hence their is a contradiction and your original statement is wrong.
I hope this helps.
Bob
answered Jan 13 at 23:05
BobBob
938515
938515
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3072509%2fprobability-proof-check-my-answer%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
$begingroup$
$P(A)$ and $P(B)$ are numbers. How do you define $P(A)cap P(B)$?
$endgroup$
– ajotatxe
Jan 13 at 20:58
$begingroup$
Indeed as user ajotatxe remarks: already in the first line, the expression “$P(A)cap P(B)$” is meaningless since $P(cdot)$ is a number and $cap$ is a set operation.
$endgroup$
– LoveTooNap29
Jan 13 at 21:04
$begingroup$
You have assumed that $A$ and $B$ are independent events, but there is no need to.
$endgroup$
– user1337
Jan 14 at 21:12