By selling two transistors for $Rs600$, each a shopkeeper gains $20$ percent on one transistor and loses $20$ percent on the other.
Find :
profit or loss percent on the whole.

Let the cost price be $x_1$ for the transistor gaining $20\%$:

$20\%$ gain $⟹x_1+\frac{20x_1}{100}=600$

$1.2x_1=600⟹x_1=500$

Let the cost price be $x_2$ for the transistor losing $20\%$:

$20\%$ loss $⟹x_2-\frac{20x_2}{100}=600$

$0.8x_2=600⟹x_2=750$

So,

Total C.P of both the transistors $=x_1+x_2=500+750=₹1250$

Total S.P of both the transistors $=600+600=₹1200$

We know that

Total loss = C.P – S.P

Substituting the values

$=1250–1200$

$=₹50$

So the loss percent $=(loss\times 100)/C.P$

Substituting the values

$=(50\times 100)/1250$

$=4\%$