S1 Probability question Watch

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#1
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#1
Hello
i need help with a question on probability, i have no idea where to start :confused:
probability's always been my weak point so if anyone could help me out here i'd be thankful

Question
80 Mathematic students were asked which A2 Science courses they were intending to take.

40 intend to take biology
35 intend to take chemistry
23 intend to take physics

28 will then be studying Biology and chemistry, 15 Biology and physics, 12 chemistry and physics and 7 will be studying all three

One student is selected at random. Find the probability that this student
a) intends to study only one of the subjects

a) was the first question out of four but i think if i get part a) i will be able to do the rest

ok thanks to anyone who replies
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Glutamic Acid
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Have you tried drawing a Venn diagram?
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hmmm yep i've tried...but im not sure how to i drew three circles but im guessing that's wrong and then i got confused on how to get it all to equal 80
isnt there another way? do i have to do a venn diagram?
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Frater
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Remmber the wording of the question.... mathematic students, so the number inside the circles wont add upto 80.

What does the book say for the answer to part a) i get 10/80
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the answers 9/80
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Frater
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yup, I get that too my calculation error. Ok, start with the 3 circles, put the 7 in the middle.... now if 7 people are doing all 3, you should take it away from the number of people studying both of chem +bio ect. P(BC) and P(BP) and P(CP). You got that?
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#7
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yep ive got the answer thank you so much
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