By selling a tape-recorder for $\text{Rs. }1900$, I lost $5\%$. What percent shall I gain by selling it for $\text{Rs. }2080$?

First, find the Cost Price ($\text{C.P.}$) of the tape-recorder.
Given: ${\text{Selling Price (S.P.)}}_1=\text{Rs. }1900$ and $\text{Loss}=5\%$.

$${\text{S.P.}}_1=95\%\text{ of C.P.}$$

$$1900=\frac{95}{100}\times \text{C.P.}$$

$$\text{C.P.}=\frac{1900\times 100}{95}=20\times 100=\text{Rs. }2000$$

Now, a new selling price is given: ${\text{S.P.}}_2=\text{Rs. }2080$.

$$\text{Gain}={\text{S.P.}}_2-\text{C.P.}=2080-2000=\text{Rs. }80$$

Calculate the gain percentage:

$$\text{Gain }\%=\frac{\text{Gain}}{\text{C.P.}}\times 100$$

$$\text{Gain }\%=\frac{80}{2000}\times 100=4\%$$