Question 23
The average of $\overline{abc}$, $\overline{ab}$, $\overline{bc}$, and $\overline{ca}$ is $M$. If $\overline{ab}$ is removed, the average of the remaining three numbers becomes $N$. If the difference between $N$ and $M$ is $40$, what is the maximum possible value of $\overline{abc}$?