We will be using the fact that , where
is the probability that the first bulb works and
is the probability that the second bulb works.
The probability that the first bulb works is . However, when we take one out (given that the first bulb works) we now have 19 working bulbs and 4 bad ones. This means that the probability that the second bulb works is
.
Now, we can find our final probability:
Answer:
Part 1)
Part 2)
Part 3)
Step-by-step explanation:
Part 1) Find the measure of angle ECF
we know that
CF is tangent at point C
so
the radius EC is perpendicular to the tangent CF
therefore
Part 2) Find the measure of angle AKB
we know that
The measure of the interior angle is the semi-sum of the arcs comprising it and its opposite
substitute the values
Part 3) Find the measure of angle ACF
we know that
The inscribed angle is half that of the arc it comprises
substitute the values