let 'x' be the cost of 1 pencil
let 'y' be the cost of 1 pen
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two pencils & 3 pens is 50
2x + 3y = 50 -equation 1
3 pencils & 2pens is 45
3x + 2y = 45 -equation 2
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multiply equation 1 with 2 and equation 2 with 3
(2x + 3y = 50) × 2
4x + 6y = 100 -equation 1'
(3x + 2y = 45) × 3
9x + 6y = 135 -equation 2'
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subtract equation 1 from equation 2
9x + 6y = 135
- 4x + 6y = 100
5x = 35
x = 7
therefore one pencil costs 7 pesos
NOTE: There's no need to get the value of y since you are only asked of the cost of 1 pencil which is x
