Let total sales be \( x \).
Under the first scheme:
\[
\text{Commission} = 5% \times x = 0.05x
\]
Under the new scheme:
- Fixed salary = Rs. 1,000
- Commission on \( x - 4,000 \) = \( 2.5% \)
\[
1,000 + 0.025(x - 4,000)
\]
The difference between the two earnings is Rs. 600:
\[
1,000 + 0.025(x - 4,000) = 0.05x + 600
\]
\[
1,000 + 0.025x - 100 = 0.05x + 600
\]
\[
900 + 0.025x = 0.05x + 600
\]
\[
900 - 600 = 0.05x - 0.025x
\]
\[
300 = 0.025x
\]
\[
x = \frac{300}{0.025} = 12,000
\]
Thus, the total sales were Rs. 12,000.