On decreasing the price of a fan by 30 percent, its sales increases by 40 percent. What will be the percentage decrease in its revenue?

2 percent decrease

Revenue = Sale × Price

                             Initial      :         Final

Price                        10         :          7

Sale                          5          :         7

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Revenue                   50         :         49

 Required percentage = \(\frac{1}{50}\)  × 100 = 2%