Step 1: Assume the Marked Price (M.P.) = \rupee100.
When discount is 22%, Selling Price (S.P.) = \( 100 - 22\) = \rupee78
Let Cost Price (C.P.) be \( x \). Given profit = 17%:
\[
\frac{78 - x}{x} \times 100 = 17 \quad \Rightarrow \quad \frac{78 - x}{x} = \frac{17}{100}
\]
\[
\Rightarrow 100(78 - x) = 17x \quad \Rightarrow \quad 7800 - 100x = 17x
\]
\[
\Rightarrow 7800 = 117x \quad \Rightarrow \quad x = \frac{7800}{117} = \rupee66.67
\]
Step 2: When discount is 18%, new S.P. = \rupee82
\[
\text{New profit%} = \frac{82 - 66.67}{66.67} \times 100 \approx \frac{15.33}{66.67} \times 100 \approx 23%
\]
Step 3: Difference in profit percentage = \( 23% - 17% = \boxed{6%} \)