Ajacket is reduced by 40% in a sale. the cost of the jacket is now £126. pauline says " 40% of £126 is £50.40. so the jacket originally cost £176.40." pauline is wrong explain why.

  Pauline used the wrong base to compute the discount.

Step-by-step explanation:

Pauline is wrong because she figured the discount on £126 instead of the original cost. The actual discount is figured on the original cost, so £126 represents 60% of that cost.

The original cost is perhaps best found by dividing the sale price by 0.60 to get £210. Then we can check by computing the discount as 40% of £210, or £84, leaving a sale price of £210 -84 = £126.