How do you calculate successive percentages?

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When there are sales we are often faced with shop windows advertisements calling our attention about discounts like 20% + 30%. But is this kind of discount equivalent to 50% or is it different? In this case we are faced with a successive discount. The application of these two successive percentages, this is, one after the other, is different from the application of their addition. This is easy to understand if we have in mind that the base of incidence of the second percentage is inferior to the base of incidence of the first percentage. So, the final discount does not correspond, in this case, to the half of the price. Most of us has little mathematical knowledge and do this fact this marketing technique uses a “deceitful” kind of advertising, leading us to believe that we are buying something half the price! But in reality things are too different!

calculate percentages

Could you give us a real example?

Of course I could. Here we go. Let’s suppose we want to buy a coat whose initial price is 150€. This price will suffer a successive discount of 20% + 30%. Let’s calculate the final price we have to pay:

  • `20% = 0.20`
  • The value of the first discount will be: `150 xx 0.20 = 30€`
  • The price to pay after the first discount is: `150 - 30 = 120€`
  • `30% = 0.30`
  • The value of the second discount will be: `120 xx 0.30 = 36€`
  • The price to pay after the second discount will be: `120 - 36 = 84€`

If a discount of 50% was directly applied to the coat, the final value would be quite different!

  • `50% = 0.50`
  • The value of the discount would be :`150 xx 0,50 = 75€`
  • The price to pay after the discount would be: `150 - 75 = 75€`


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