JAMB 2018 · UTME · Q1

Find $x$ and $y$ respectively in the subtraction below.

$\begin{array}{rcccc} & 4 & 2 & 4 & 3 \\ - & 1 & 3 & x & 4 \\ \hline & y & 3 & 4 & 4 \end{array}$

Worked solution (try it first)

The digits are all below 5, so work in base 5.
Units: $3 < 4$ , so borrow 5: $8 - 4 = 4$ .
Fives: $4 - 1 = 3$ is less than $x$ , so borrow again: $8 - x = 4$ , giving $x = 4$ .
25s: $2 - 1 = 1 < 3$ , so borrow: $6 - 3 = 3$ . 125s: $4 - 1 - 1 = 2$ , so $y = 2$ .
So $x = 4$ and $y = 2$ , option C.