In a shop, 80% of the articles are sold at a profit of 10% and the remaining at a loss of 40%. What is the overall profit/loss ?

Let the total C.P. of all the articles be Rs. x.
Then,
C.P. of 80% of the articles = 80% of Rs. x.
$$ = {\text{Rs}}.\frac{{4x}}{5}$$
C.P. of the remaining articles
$$\eqalign{ & = {\text{Rs}}.\left( {x - \frac{{4x}}{5}} \right) \cr & = {\text{Rs}}.\frac{x}{5} \cr & {\text{Total S}}{\text{.P}}{\text{.}} \cr & = Rs.\left( {110\% {\text{ of }}\frac{{4x}}{5} + 60\% {\text{ of }}\frac{x}{5}} \right) \cr & = {\text{Rs}}.\left( {\frac{{22x}}{{25}} + \frac{{3x}}{{25}}} \right) \cr & = {\text{Rs}}{\text{. }}x. \cr} $$
Since C.P. = S.P. there is no profit no loss