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My probability question #1 (1 Viewer)

snoopy05

snoopy05

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Oct 23, 2004
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school's janitor's
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HSC
2005
a box contains 10 chocolates. three of the chocolates have caramel centers, and other 7 has mint centers. hugo selects 3 chocolate from the box randomly,

what is the probability that hugo eats atleast 2 caramel chocolates


the answer is 11 / 60

(how can we do this without using tree diagram?)
or is it best for us to use tree diagram? .....(assume that i dont have the ability to visualise things very good)
 
S

SaHbEeWaH

Member
Joined
Aug 7, 2004
Messages
42
P(selects 2 caramel chocolates): 3/10 * 2/9 * 7/8 * 3C2 = 7/40

P(selects 3 caramel chocolates): 3/10 * 2/9 * 1/8 = 1/120

Therefore, P(selects at least 2 caramel) = 7/40 + 1/120 = 11/60

or ...

P(selects no caramel chocolates): 7/10 * 6/9 * 5/8 = 7/24

P(selects 1 caramel chocolate): 7/10 * 6/9 * 3/8 * 3C1 = 21/40

Therefore, P(selects at least 2 caramel) = 1 - 7/24 - 21/40 = 11/60
 
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