WAEC 2020 · Paper 1 · Q10

Given that $2x + 3y - 10 = 0$ and $3x = 2y - 11$ , calculate the value of $(x - y)$ .

Worked solution (try it first)

Write both as $ax + by = c$ : $2x + 3y = 10$ and $3x - 2y = -11$ .
Multiply the first by 2 and the second by 3: $4x + 6y = 20$ and $9x - 6y = -33$ .
Adding gives $13x = -13$ , so $x = -1$ .
Then $3y = 10 - 2(-1) = 12$ , so $y = 4$ .
So $x - y = -1 - 4 = -5$ , option D.