Quantitative Aptitude :: Profit and Loss - Discussion

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Explanation:
SP=144
Lets assume cost price of watch= Rs. x
so profit %=x
C.P.= (100/(100+gain%))*S.P. -----(formula to get CP)
x=(100/100+x) *144
=> x^2+100x=14400
=> x^2+180x-80x-14400=0
=> (x+180) (x-80)=0
=> x=-180
=> x=80