Explanation

Say the item costs $100. After the first 10% discount, the item costs $90. After the second, the item costs $81 (the new discount is only $9, or 10% of 90). After the third discount, the item costs $81 – $8.10 = $72.90.

What is the trend here? The cost goes down with each discount, yes, but the discount itself also gets smaller each time; it is only a $10 discount the very first time. The total of the five discounts, then, will be less than $50.

If the item costs $100 to start, then the value for Quantity B will be $50, or a total discount of $50. This is greater than the total discount described for Quantity A.

Finally, make sure to answer (A) for the higher price—don’t accidentally pick (B) for the “better deal”!
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Let item price = 100$

Quantity A:
100*0.9=90
90*0.9=81
81*0.9=72.9
72.9*0.9=65.61
65.61*0.9=59.049

Quantity B:
100*0.5=50