Question:
Three unbiased coins are tossed once. Find the probability of getting
at most 2 tails or at least 2 heads
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 heads or at most two tails. So, desired outputs are TTH, THT, HTT, THH, HTH, HHT, HHH
Total no.of outcomes are 8 and desired outcomes are 7
Probability of getting at most 2 tails or at least 2 heads $=\frac{7}{8}$
Conclusion: Probability of getting at least two heads or at most two tails is $\frac{7}{8}$