Answer
First two lectures start at $9:00$. First, lecture overlaps only with the lecture $3$ whereas the second lecture overlaps with the lectures $3$ and $4$.
So, we choose lecture $1$ followed by lecture $4$. we can not add lectures $5$ and $6$ since lecture $4$ overlaps with them.
we had chosen lecture $2$ instead we would get the sequence of lectures as $ 2-5-5$ by which h we could have ended up and a greater number of lectures.
Work Step by Step
Consider the following set of lectures
$1)9:00−10:00 $
$2)9:00−11:00$
$3)9:30−10:30$
$4)10:00−12:00$
$5)11:00−11:30$
$6)11:30−12:30$
First two lectures start at $9:00$. First, lecture overlaps only with the lecture $3$ whereas the second lecture overlaps with the lectures $3$ and $4$.
So, we choose lecture $1$ followed by lecture $4$. we can not add lectures $5$ and $6$ since lecture $4$ overlaps with them.
we had chosen lecture $2$ instead we would get the sequence of lectures as $ 2-5-5$ by which h we could have ended up and a greater number of lectures.
