HI! Friends I have a problem in Set Theory Formula , Please Help me understand it
(reunion of A, B and C) = (total in A) + (total in B) + (total in C) - (total in exactly 2 groups) - 2(total in all 3 groups)
we have one more formula
# - Intersection ( I m not able to find the sign of intersection )
n ( A U B U C ) = n ( A ) + n ( B ) + n ( C ) - n ( A # B ) - n ( B # C ) - n ( C # A ) + n ( A # B # C )
I know both of the formula are same but i am not to figure out the difference How they are same,
Can any body please help me................
Venn Diagram
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- goyalsau
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- goyalsau
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guys help
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goyalsau wrote:HI! Friends I have a problem in Set Theory Formula , Please Help me understand it
(reunion of A, B and C) = (total in A) + (total in B) + (total in C) - (total in exactly 2 groups) - 2(total in all 3 groups)
we have one more formula
# - Intersection ( I m not able to find the sign of intersection )
n ( A U B U C ) = n ( A ) + n ( B ) + n ( C ) - n ( A # B ) - n ( B # C ) - n ( C # A ) + n ( A # B # C )
I know both of the formula are same but i am not to figure out the difference How they are same,
Can any body please help me................
Refer to the above image. If it is not clear then follow me...
Total in A - Blue
Total in B - Red
Total in C - Green
Total in (A ∩ B) = (Red + Blue) = Magenta
Total in (B ∩ C) = (Red + Green) = Yellow
Total in (A ∩ C) = (Blue + Green) = Cyan
Total in (A ∩ B ∩ C) = (Cyan + Magenta + Yellow) = (2*Red + 2*Blue + 2*Green) = White
Only in A and B = Magenta - White = (A ∩ B) - (A ∩ B ∩ C)
Only in B and C = Yellow - White = (B ∩ C) - (A ∩ B ∩ C)
Only in A and C = Cyan - White = (A ∩ C) - (A ∩ B ∩ C)
Therefore only in exactly two groups = Only in A and B + Only in B and C + Only in A and C = (A ∩ B) - (A ∩ B ∩ C) + (B ∩ C) - (A ∩ B ∩ C) + (A ∩ C) - (A ∩ B ∩ C) = (A ∩ B) + (B ∩ C) + (A ∩ C) - 3(A ∩ B ∩ C)
Only in A = Blue - Magenta - Cyan + White = A - (A ∩ B) - (A ∩ C) + (A ∩ B ∩ C)
Only in B = Red - Magenta - Yellow + White = B - (A ∩ B) - (B ∩ C) + (A ∩ B ∩ C)
Only in C = Green - Yellow - Cyan + White = C - (A ∩ C) - (B ∩ C) + (A ∩ B ∩ C)
(White is added as Magenta, Cyan and Yellow also contains white in them, thus white is subtracted twice)
Now, 1st formula:
- (A U B U C) = (total in A) + (total in B) + (total in C) - (total in exactly 2 groups) - 2(total in all 3 groups)
(A U B U C) = A + B + C - [(A ∩ B) + (B ∩ C) + (A ∩ C) - 3(A ∩ B ∩ C)] - 2*(A ∩ B ∩ C)
(A U B U C) = A + B + C - (A ∩ B) - (B ∩ C) - (A ∩ C) + (A ∩ B ∩ C)]
Hope it helps.
Last edited by Rahul@gurome on Tue Nov 16, 2010 8:50 pm, edited 1 time in total.
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- Tani
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The second formula has an error. The last term should be to subtract twice the number that are in all three groups. Also, both formulas should include a term that adds in the number of items that are not in any of the groups. THat would give you the totals.
What you are doing is adding all the items, then subtracting those that are counted twice (i.e. in A and B, A and C, or B and C) and then subtracting two times the number of items that are in all three.
It may be easier to understand looking at the formula for combining two sets.
Total = A + B - both + neither
subtracting items in "both" compensates for the fact that they are counted twice. Adding "neither" picks up items that are not in any of the designated categories, but are included in the total.
Example = school has 100 students
45 take Spanish
63 take French
15 take neither
100 = 45 + 63 + 15 - B
B= number taking both French and Spanish. Here that would equal 23 students. You can show the same situation using a Venn diagram.
What you are doing is adding all the items, then subtracting those that are counted twice (i.e. in A and B, A and C, or B and C) and then subtracting two times the number of items that are in all three.
It may be easier to understand looking at the formula for combining two sets.
Total = A + B - both + neither
subtracting items in "both" compensates for the fact that they are counted twice. Adding "neither" picks up items that are not in any of the designated categories, but are included in the total.
Example = school has 100 students
45 take Spanish
63 take French
15 take neither
100 = 45 + 63 + 15 - B
B= number taking both French and Spanish. Here that would equal 23 students. You can show the same situation using a Venn diagram.
Tani Wolff
- goyalsau
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Rahul, Thanks lot for the detailed explanation, But it would have been wonderful , IF i able to see the picture as well.Rahul@gurome wrote:
Refer to the above image.
I am not able to open your picture, it says The file format is unsupported..
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@goyalsau: Updated the image. See if it helps.
Rahul Lakhani
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