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# stats watch

1. in a school of 400 students, 250 play a musical instrument and 100 sing in the choir.

the probability that a student chosen at random neither plays a musical instrument nor sings in the choir is 1/5.

(i) how many students both sing in the choir and play a musical instrument?

i did P(A' or b')=1- (1/5)=4/5

(ii) find the probability that a student chosen at random sings in the choir but does not play an instrument?

(iii) find the probability that a member of the choir chosen at random does not play an instrument?

(iv) find the probability that someone who does not play an instrument is in the choir..

I'm struggling to draw a venn diagram to represent this information i can't do either a two way table or tree diagram because i can't do part (i) and don;t have enough info..

thank you.
2. (Original post by Student#123)
in a school of 400 students, 250 play a musical instrument and 100 sing in the choir.

the probability that a student chosen at random neither plays a musical instrument nor sings in the choir is 1/5.

(i) how many students both sing in the choir and play a musical instrument?

i did P(A' or b')=1- (1/5)=4/5

(ii) find the probability that a student chosen at random sings in the choir but does not play an instrument?

(iii) find the probability that a member of the choir chosen at random does not play an instrument?

(iv) find the probability that someone who does not play an instrument is in the choir..

I'm struggling to draw a venn diagram to represent this information i can't do either a two way table or tree diagram because i can't do part (i) and don;t have enough info..

thank you.
400 students
250 play musical instruments
100 sing in choir
80 does neither (1/5 of total)
So 320 does any one
250 + 100=350 so 30 must do both.

Its easier if you draw a Venn diagram and try filling it up logically.

You're first answer is wrong, I think, because that's the probability that a students does any of the two not both, right?
3. (Original post by StUdEnTIGCSE)
400 students
250 play musical instruments
100 sing in choir
80 does neither (1/5 of total)
So 320 does any one
250 + 100=350 so 30 must do both.

Its easier if you draw a Venn diagram and try filling it up logically.

You're first answer is wrong, I think, because that's the probability that a students does any of the two not both, right?
ok..can u help me with the other bits plz...

why is (ii) not 1/4 ..?
4. is this too difficult for u guys too?

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Updated: April 17, 2013
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