By selling two transistors for Rs. $600$ each, a shopkeeper gains $20$ percent on one transistor and loses $20$ Percent on the other,
Find: (i) C.P.of each transistor.
(ii) total C P and total S.P. of both the transistors
(iii) profit or loss percent on the whole.

Let $C{P}_1$ & $C{P}_2$ be the cost price of $1^{st}$ transistors and $2^{nd}$ transistors respectively

selling price of each transistors, $S{P}_1=RS600$

Gain of one transistors = 20%

$\Rightarrow \frac{S{P}_1-C{P}_1}{C{P}_1}\times 100=20.$

$\Rightarrow \frac{600-C{P}_1}{C{P}_1}\times 100=20.$

$\Rightarrow 600-C{P}_1=\frac{20}{100}C{P}_1$

$\Rightarrow 600=\frac{20}{100}C{P}_1+C{P}_1$

$\Rightarrow \frac{120}{100}C{P}_1=600$

$\Rightarrow C{P}_1=\frac{600\times 100}{120}$

$\Rightarrow C{P}_1=Rs500$

and loss of other transistors = 20 %

$\Rightarrow \frac{C{P}_2-S{P}_1}{C{P}^1}\times 100=20$

$\Rightarrow C{P}_2-600=\frac{20}{100}C{P}_2$

$\Rightarrow C{P}_2\frac{-20}{100}C{P}_2=600$

$\Rightarrow \frac{80}{100}C{P}_2=600$

$\Rightarrow C{P}_2=\frac{600\times 100}{80}$

=RS 750

cost price of $1^{st}$ transistors = Rs 1350

Cost price of $2^{nd}$ transistors = Rs 750.

Total cost price ,CP = Rs (600+750) = 1350

Total selling price SP = Rs (600+600) = Rs 1200.

loss on the whole = $\frac{CP-SP}{CP}\times 100$

$\frac{1350-1200}{1350}\times 100$

$\frac{150}{1350}\times 100$

= 11.11 % (approx.)