A shopkeeper sells one transistor for $Rs.840$ at a gain of $20$% and another for $Rs.960$ at a loss of $4$%. His total gain or loss percent is

The correct option is B $5\frac{15}{17}$% gain
C.P. of $1^{st}transistor=Rs.(\frac{100}{120}\times 840)=Rs.700$.
C.P. of $2^{nd}transistor=Rs.(\frac{100}{96}\times 960)=Rs.1000$
So, total $C.P.=Rs.(700+1000)=Rs.1700$.
Total $S.P.=Rs.(840+960)=Rs.1800$.
$\therefore Gain$% $=(\frac{100}{1700}\times 100)$% $=5\frac{15}{17}$%