Question:
Three unbiased coins are tossed once. Find the probability of getting at least 2 tails
Solution:
We know that,
Probability of occurrence of an event
$=\frac{\text { Total no.of Desired outcomes }}{\text { Total no.of outcomes }}$
Let $\mathrm{T}$ be tails and $\mathrm{H}$ be heads
Total possible outcomes = TTT, TTH, THT, HTT, THH, HTH, HHT, HHH
Desired outcomes are at least two tails. So, the desired outputs are
TTH, THT, HTT, TTT
Total no.of outcomes are 8 and desired outcomes are 4
Therefore, the probability of getting at least 2 tails $=\frac{4}{8}$
$=\frac{1}{2}$
Conclusion: Probability of getting at least two tails is $\frac{1}{2}$