The manufacturer of tyres is offering a 10% discount on the price
of its tubeless tyres. Some retailers are offering additional discounts. If a
retailer offers an additional 20% discount, then what is the total discount available
at that retailer?

○○ 10%
○○ 25%
○○ 28%
○○ 30%
○○ 35%

If we REDUCE a price by 10%, then the reduced price is 90% of the original price.
Likewise, if we REDUCE a price by 20%, then the reduced price is 80% of the original price.
If we REDUCE a price by 30%, then the reduced price is 70% of the original price.
.....etc.
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Let $100 be the original price.
So, a 10% reduction means the new price = (0.9)(100) = $90
A further 20% reduction means the new price = (0.8)(0.9)(100) = $72
This represents a $28 discount off the original $100
28/100 = 28%

Answer:

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Discount = 1-0.9*0.8=1-0.72=0.28=28%
Answer choice C.

This is an example in the lower range that wants to trick people into forgetting about the joint effect of the two discounts and thus simply adding them to get 30%.
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