Video Transcript
For two independent events 𝐴 and
𝐵, where the probability of 𝐴 is 0.45 and the probability of 𝐵 is 0.3, calculate
the probability of 𝐴 given the complement of 𝐵.
The vertical line in our question
means given that. The hash mark means the
complement. This means the probability of 𝐵
not occurring. In order to answer this question,
we need to recall some of our probability formulae. The probability of the complement
of 𝐴 is equal to one minus the probability of 𝐴. The probability of 𝐴 given 𝐵 is
equal to the probability of 𝐴 intersection 𝐵 divided by the probability of 𝐵. We are also told in this question
that our events are independent. For independent events, the
probability of 𝐴 intersection 𝐵 is equal to the probability of 𝐴 multiplied by
the probability of 𝐵.
As the probability of 𝐵 is 0.3,
the complement of this will be one minus 0.3. The probability of 𝐵 not occuring
is 0.7. As our events are independent, the
probability of 𝐴 occurring and 𝐵 not occurring is equal to 0.45 multiplied by
0.7. We multiply the probability of 𝐴
by the probability of the complement of 𝐵. This is equal to 0.315. We can, therefore, calculate the
probability of 𝐴 occurring given that 𝐵 does not occur by dividing 0.315 by
0.7. We divide the probability of 𝐴
occurring and 𝐵 not occurring by the probability of 𝐵 not occurring. This is equal to 0.45.
