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A survey of 100 students produced the following statics: 32 study mathematics, 20 study physics, 45 study Biology, 15 study mathematics and biology, 7 study mathematics and physics, 10 study physics and Biology, 30 do not study any of the three subjects

1, Present the information in a Venn Diagram
ii, Find the number of students who study all the three subjects
iii, Take exactly one of the three subjects

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3 answers

  1. We don't know the intersection of all three circles, so label it x
    Now go to the intersection of two of the circles, say, the M and B circles
    It says that sum is 15, but we have already counted x of them, so in the remaining part of the football-shaped region is 15-x
    Do that for the other two intersection of pairs to have 10-x and 7-x

    Now go to the whole circles, start with M
    We have already counted, 15-x, x, and 7-x
    or 22-x
    But the whole math circle contains 32, so the open part must be 32-(22-x) = 10+x
    Do the same with the other whole circles and get
    20+x and 3+x

    Now add them all up.
    We can use a short-cut here, we know that everything in the Math circle is 32, so ..

    32 + 10-x + 20+x + 3+x = 70
    x = 5

    ii) 5 take all three subjects
    ii) add up all the parts in the outer parts of the circle which do not intersect with any other circles
    that is,
    Math only = 27
    Biology only = 25
    Physics only = 8

    or

    using the formula:
    N(M or P or B) = N(M) + N(B) + N(P) - N(M and P) - N(M and B) - N(P and B) + N(M and P and B)
    70 = 32+45+20 - 7 - 15 -10 + x
    x= 5

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  3. Maths only is 25 because 45+5-25
    Bio only is 15 because 32+5-22
    Physics only is 8 because 20+5-17

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