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Probability - Tossing a coin

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by Uva@90 » Sat May 16, 2015 9:37 am
Hi All,

How many times was a fair coin tossed?

(1) If the coin has been tossed 4 times fewer, the probability of getting heads on every toss would have been (1/8)
(2) When a coin is tossed the number of times, the number of different possible sequences of heads and tails is 128.

OA :D

Regards,
Uva
Known is a drop Unknown is an Ocean
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by theCEO » Sat May 16, 2015 1:26 pm
Uva@90 wrote:Hi All,

How many times was a fair coin tossed?

(1) If the coin has been tossed 4 times fewer, the probability of getting heads on every toss would have been (1/8)
(2) When a coin is tossed the number of times, the number of different possible sequences of heads and tails is 128.

OA :D

Regards,
Uva
1.
probability of getting head on 1 toss = 1/2
probability of getting heads on 2 tosses = 1/2 x 1/2 = 1/4
probability of getting heads on 3 tosses = 1/2 x 1/2 x 1/2 = 1/8
4 times fewer = 3 tosses
x - 4 = 3, therefore x = 4+3=7; sufficient

2.
when a coin is toss 1 time, the number of outcome is 2
when a coin is toss 2 times, the number of outcome is 2 x 2 = 4 = 2^2
the general formula for the possibilities is 2^n where n is the number of tosses
128 could be rewritten as 2^7
2^n = 2^7 ->n=7
therefore number of tosses = 7; sufficient
answer = d
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