70 pounds was the original price of the chair before the sale.
Original price = 100%
discount rate = 10%
New price = 90%
The new price of the chair is 63 pounds. It is 90% of the original price. Therefore, 63 pounds is divided by 90% to get the original price.
63 / 90% = 70 original price
70 * 10% = 7 sales discount
70 - 7 = 63 discounted price