Question

In order to get at least once a head with probability greater than or equal to 0.9, the number of times a coin needs to be tossed is:

• A. 3
• B. 4
• C. 5
• D. None

Answer 1

The correct option is B 4

$1-(\frac{1}{2}{)}^n\ge 0.9\Rightarrow 2^n\ge 10\Rightarrow n\ge 4.$