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14.Probability
hard
In order to get at least once a head with probability $ \ge 0.9,$ the number of times a coin needs to be tossed is
A
$3$
B
$4$
C
$5$
D
None of these
Solution
(b) Probability of getting at least one head in $n$ tosses
$ = 1 – {\left( {\frac{1}{2}} \right)^n} \ge 0.9 $
$\Rightarrow {\left( {\frac{1}{2}} \right)^n} \le 0.1 $
$\Rightarrow {2^n} \ge 10 \Rightarrow n \ge 3$
Hence least value of $n = 4.$
Standard 11
Mathematics
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