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pws
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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 17:56
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Tommy tosses a coin four times. What is the probability that he gets heads exactly twice?



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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 18:03
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What method did you use to solve the question?
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CHEN
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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 18:10
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coin : head and toe = 2 incidents
all incidents for 4 tosses = 2*2*2*2 = 16 incidents

get head 2 times
first 1 incident of head
second 1 incident of head
third 2 incidents
fourth 2 incidents

probability = (1*1*2*2)/( 16) = 0.25 :)

If there is anything wrong with this please explain
since I make many simple mistakes in Probability
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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 18:13
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CHEN
coin : head and toe = 2 incidents
all incidents for 4 tosses = 2*2*2*2 = 16 incidents

get head 2 times
first 1 incident of head
second 1 incident of head
third 2 incidents
fourth 2 incidents

probability = (1*1*2*2)/( 16) = 0.25 :)

If there is anything wrong with this please explain
since I make many simple mistakes in Probability
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HHTT
Ways of arrange H and T..
(4*3*2*1)/(2!*2!) = 6
6/16 = 3/8
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CHEN
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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 18:24
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oh yes you are right Mr. freetheking

:oops: what a mistake !
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Professor
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Tommy tosses a coin four times. What is the probability 01 Aug 2006, 18:57
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pws
Tommy tosses a coin four times. What is the probability that he gets heads exactly twice?
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the question as given is not clear, however use of binominal formule is better if the coin is a fair one: (nCk) (p^k) (1-p)^(n-k).

= 4C2 * (1/2)^2 * (1/2)^2
= 6 (1/4)(1/4)
= 6/16
= 3/8
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Tommy tosses a coin four times. What is the probability 02 Aug 2006, 00:19
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Another way

Ways exactly twice heads come

HHTT = 1/16
HTHT = 1/16
HTTH = 1/16
THHT = 1/16
THTH = 1/16
TTHH = 1/16

P = 6* 1/16 = 3/8
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Tommy tosses a coin four times. What is the probability 02 Aug 2006, 00:26
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jaynayak
Another way

Ways exactly twice heads come

HHTT = 1/16
HTHT = 1/16
HTTH = 1/16
THHT = 1/16
THTH = 1/16
TTHH = 1/16

P = 6* 1/16 = 3/8
Show more

This is Ok for small count. If question says
Tommy tosses a coin 20 times. What is the probability that he gets heads exactly 12 times?

Then this approach is not good.



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Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
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