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AlexFokin [52]
3 years ago
15

Determine the sign of cos pi divided by seven without using a calculator.

Mathematics
1 answer:
7nadin3 [17]3 years ago
3 0
Check the picture below.

now, when you get a fraction of π for the angle, is just really like grabbing π and dividing it in that many pieces, and the angle, is a fraction of π and therefore on those pieces.

π/7 is clearly less than 7π/7 which is π, notice the 7-pieces split in the picture.

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A certain virus infects one in every 400 people. A test used to detect the virus in a person is positive 90% of the time if the
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Answer:Given:

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By the law of total probability,

P(B)=P(B|A)*P(A)+P(B|A)*P(~A)

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Note: get used to working in fraction when doing probability.

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By Baye's Theorem,

P(A|B)

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(b) Find P(~A|~B)

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P(~A)=1-P(A)=399/400

P(~B)=1-P(B)=133/136

P(A∩B)

=P(B|A)*P(A) [def. of cond. prob.]

=9/10*(1/400)

=9/4000

P(A∪B)

=P(A)+P(B)-P(A∩B)

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=P(~A∩~B)/P(~B)

=P(~A∪B)/P(~B)

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=(3591/4000) ÷ (449/500)

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The results can be easily verified using a contingency table for a random sample of 4000 persons (assuming outcomes correspond exactly to probability):

===....B...~B...TOT

..A . 9 . . 1 . . 10

.~A .399 .3591 . 3990

Tot .408 .3592 . 4000

So P(A|B)=9/408=3/136

P(~A|~B)=3591/3592

As before.

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