Question

There are $100$ students in a college class of which $36$ are boys studying and $13$ girls not studying statics. If there are $55$ girls in all, the probability that a boy picked up at random is not studying statics, is $\frac{a}{b}$, find $a+b$

Answer 1

Number of students $=100$
Number of girls $=55$
$\therefore$ Number of boys $=100-55=45$
Out of $45$ boys $36$ boys are studying Statistics.
$\therefore$ Number of boys not studying Statistics $=45-36=9$
$\therefore$ Number that a boy picked up at random is not studyng Statistics $=\frac{9}{45}=\frac{1}{5}.$