Let cost price of one article be c and selling price of one article be s.

We need to find profit/loss% which is equal to ((s-c)/c) x 100 = (s/c - 1) x 100

Given that 20c = 25s. Then s/c = 4/5

Profit% = (4/5 - 1) x 100 = -20%

Note: It is preferable to use as few variables as possible but in situations where cp of n articles = sp of m articles, it is better to use different variables for clarity.

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