we know that
The probability of an event is the ratio of the size of the event space to the size of the sample space.
The size of the sample space is the total number of possible outcomes
The event space is the number of outcomes in the event you are interested in.
so
the probability is equal to
P=size of the event space/size of the sample space
In this problem
size of the sample size=area of the rectangular dartboard=
size of the event space=area of the triangular part=
<u>Convert to percentage</u>
therefore
<u>the answer is</u>