# The minimum number of times one has to toss a fair coin so that the probability of observation at least one head is at least 90% is : Option 1) $5$ Option 2) $3$ Option 3) $4$ Option 4) $2$

Let x fair coin tossed 'n' times the P( at least one head)

$=1-P$ ( all tail)

$=1-\left ( \frac{1}{2} \right )^{n}>\frac{90}{100}$

$\Rightarrow \left ( \frac{1}{2} \right )^{n}<\frac{1}{10}$

$2^{n}>10$

$n\geq 4$

Option 1)

$5$

Option 2)

$3$

Option 3)

$4$

Option 4)

$2$

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