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the guest was me....sorry i forget to login always..
Incidcentally, there is a better shortcut to approach such problems..
If two articles are sold at the same price (same SP, S), one at a profit of p% and another at a loss of p%, the NET LOSS is given by (p^2/100)%.,
The amount of of net loss = (2.p^2.S)/(100^2-p^2). If you can remember these two formulae, you can gain more time.