The price "P" has changed two times, how has it changed?
1.15x0.7xP
Well, the first time the price went up 15%.
The second time the price dropped by 30%.
So, the overall effect of the price change was:
P = 1 - [1.15 x 0.70] = 0.195 x 100 =19.50% - drop in price.
