Answer:
She was wrong in her analysis because the sales discount of 25% is the discount on the original cost of the dress and not the purchasing cost of the dress as explained below:
Explanation:
From the question:
Purchasing cost price of the dress = £30
However, this cost (£30) was after a 25% Sales Discount
It, therefore, implies that £30 is equal to 75% of the cost price
75% of the original cost price = £30
100% of the original cost price = (30 x100%)/75%
Original cost price = £40
Therefore the 25% discount / savings on the cost
= £ (40-30)
= £10
She saved £10 by buying the dress at £30 instead of the original cost of £40