Call the notebooks x, and the pencils y. 3x + 4y = $8.50 and 5x + 8y = $14.50 Then just solve as simultaneous equations: 3x + 4y = $8.50 5x + 8y = $14.50
5(3x + 4y = 8.5) 3(5x + 8y = 14.5)
15x + 20y = 42.5 15x + 24y = 43.5
Think: DASS (Different Add, Similar Subtract). 15x appears in both equations so subtract one equation from the other. Eassier to subtract (15x + 20y = 42.5) from (15x + 24y = 43.5)
(15x + 24y = 43.5) - (15x + 20y = 42.5) = (4y = 1) which means y = 0.25.
Then substitue into equation : 15x + 20y = 42.5 15x + 5 + 42.5 15x = 42.5 - 5 = 37.5 15x = 37.5 x = 2.5