If $a-1=b+2=c-3=d+4$, which is the largest among the numbers $a, b, c$ and $d$?
(a) $a$
(b) $b$
(c) $c$
(d) $d$
(e) They are all equal
The correct option is (c).

By adding 3 to all members, we get $a-1+3=b+2+3=c-3+3=d+4+3$, so that $a+2=b+5=c=d+7$, showing that $c$ is the largest of the numbers.