1.

(i) 5 pencils and 7 pens together cost 50, whereas 7 pencils and 5 pens togethercost ? 46. Find the cost of one pencil and that of one pen.

Answer»

let cost(in RS) of one pencil = x and cost (in RS) of one pen = yTherefore , according to question 5x+7y = 50 ........ (1) 7x + 5y = 46 .........(2) Multiply equation 1 by 7 and equation by 5 we get 7(5x+7y)= 7*50 35x +49y = 350 .......(3) and 5(7x +5y) = 5*46 35x +25y = 230 ....... (4)

Subtract equation 4 from equation 3 , we get 35x + 49y - 35x - 25y = 350 -230 49y -25y = 120 24y = 120 y = 120 /24 y= 5Substitute y=5 in equation 1 , we get 5x + 7*5 =50 5x+35 =50 5x = 50 - 35 5x =15 x= 15/5 x=3

Hence Cost of One Pencil = x =3 Cost of One Pen =y =5


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