Question 21
(a) Find all positive two-digit integers $\overline{ab}$ such that
$$(a+1)(b+1)=\overline{ab}+1.$$
(b) Find all positive three-digit integers $\overline{abc}$ such that
$$(a+1)(b+1)(c+1)=\overline{abc}+1.$$
$$(a+1)(b+1)=\overline{ab}+1.$$
(b) Find all positive three-digit integers $\overline{abc}$ such that
$$(a+1)(b+1)(c+1)=\overline{abc}+1.$$