Given:
Three coins are tossed.
Let the event H represents all Heads and the event K represents at least one Heads.
To find:
a. The probability that the outcome is all heads if at least one coin shows a heads.
b. P(K) = ?
c. P(H∩K) = ?
Solution:
If three coins are tossed, then the total possible outcomes are:
{HHH, HHT, HTH, HTT, THH, THT, TTH, TTT}
Total outcomes = 8
Possible outcomes for all Heads = 1
Possible outcomes for at least one Heads = 7
Let the following events:
H = all Heads
K = at least one Heads.
Then,
[tex]H=\{HHH\}[/tex]
[tex]K=\{HHH, HHT, HTH, HTT, THH, THT, TTH\}[/tex]
[tex]H\cap K=\{HHH\}[/tex]
Now,
[tex]P(K)=\dfrac{7}{8}[/tex]
[tex]P(H\cap K)=\dfrac{1}{8}[/tex]
a. The probability that the outcome is all heads if at least one coin shows a heads is:
[tex]P(H|K)=\dfrac{P(H\cap K)}{P(K)}[/tex]
[tex]P(H|K)=\dfrac{\dfrac{1}{8}}{\dfrac{7}{8}}[/tex]
[tex]P(H|K)=\dfrac{1}{7}[/tex]
Therefore, the probability that the outcome is all heads if at least one coin shows a heads is [tex]\dfrac{1}{7}[/tex].
b. [tex]P(K)=\dfrac{7}{8}[/tex]
c. [tex]P(H\cap K)=\dfrac{1}{8}[/tex]
