Question

A woman has 7 keys. only one of them will open her door. when seh arrives at the door there is no sufficient light for her to find the correct key. if she tries one key at a time and discards the keys that don't work, what is the probability that she will open the door with the first key she picks? what is the probability that it will take exactly three attempts to open the door? suppose that the first three attempts to open the door have been unsuccessful. what is the probability that she will pick the right key the fourth time?

Answer 1

Since she has seven key the probability that the first one will open the door is
$\frac{1}{7}$
if it takes three attempts to open the door,the probability is
$\frac{1}{3}$
if the three attempts would not work
then the probability that the fourth attempt will open the door is
$\frac{1}{4}$
hope this helps