Answers

2015-03-26T19:39:14+05:30
Let the no of pens=x
Total cost of the pens=Rs.80
⇒cost of each pen=Rs.80/x
If the no of pens is(x+4),then the cost of each pen is Rs 80/(x-4)
80/x-80/(x+4)=1
⇒80(x+4)-80x/x(x+4)=1-[Taking LCM]
⇒80x+320-80x=x(x+4)
⇒320=x²+4x-[cancel 80x]
⇒x²+4x-320=0
x²+20x -16x-320=0
⇒ By grouping,
 ⇒x(x+20)-16(x+20)=0
 ⇒(x+20)(x-16)=0
 ⇒(x+20)=0 or (x-16)=0
 ⇒x=-20 or x=16
 Therefore,Number of pens=x=Rs.16
Number of pens cannot be negative
Hence,-20 is rejected
Therefore,
cost of each pen=80/x=80/16
                                  =Rs.5

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