The cost of 3 notebooks and 4 pencils is $8.50. Determine the cost of one notebook and one pencil
1 answer:
Call the notebooks x, and the pencils y. <span>3x + 4y = $8.50 and 5x + 8y = $14.50 </span> <span>Then just solve as simultaneous equations: </span> <span>3x + 4y = $8.50 </span> <span>5x + 8y = $14.50 </span> <span>5(3x + 4y = 8.5) </span> <span>3(5x + 8y = 14.5) </span> <span>15x + 20y = 42.5 </span> <span>15x + 24y = 43.5 </span> <span>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) </span> <span>(15x + 24y = 43.5) - (15x + 20y = 42.5) = (4y = 1) which means y = 0.25. </span> <span>Then substitue into equation : </span> <span>15x + 20y = 42.5 </span> <span>15x + 5 + 42.5 </span> <span>15x = 42.5 - 5 = 37.5 </span> <span>15x = 37.5 </span> <span>x = 2.5 </span> <span>15x + 24y = 43.5 </span> <span>15(2.5) + 24(0.25) </span> <span>37.5 + 6 = 43.5 </span> <span>So x (notebooks) are 2.5 ($2.50) each and y (pencils) are 0.25 ($0.25) each.</span>
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