A sells an article to B at a profit of 10% B sells the article back to A at a loss of 10%. In this transaction:

Explanation:-

First Method
Let CP was 100 for A originally.
A sells article to B at 10% profit,
CP for B = 100 + 10% of 100 = 110.
Now, B sells it A again with loss 10%.
Now, CP for A this time = 110 - 10% of 110 = 99.
A makes Profit = 110 - 99 = 11.
%profit for A = ^(11*100)/₁₀₀ = 10%.

Second Method
It could be easily shown by net percentage change graphic.
100(A)==10%(Profit)==>110(B)==10%(Loss)==>99(A)

In this transaction A makes a profit of (110-99 = 11%) 11% .

[10% on selling to B and 1% profit on buying back from B].