Question:
5 pencils and 7 pens together cost Rs.50, whereas 7 pencils and 5 pens together cost Rs.46. Find the cost of one pencil and that of one pen.
Answer:
Let cost of one pencil = x and cost of one pen = y
=> 5x+7y = 50 .....................1
Again
=> 7x+5y = 46 .....................2
multiply by 7 in equation 1 and 5 in equation 2 , we get
35x + 49y = 350 ..............3
35x + 25y = 230 ..............3
Now equation 1 - equation 2, we get
24y = 120
=> y = 5
Put value of y in equation 1
5x + 7*5 = 50
=> 5x + 35 = 50
=> 5x = 50-35
=> 5x = 15
=> x = 15/5
=> x = 3
So cost of one pencil = 3 rupees
cost of one pen = 5 rupees
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