prix de départ P
augmentation de 30% = P x 30%
=> nouveau prix = P + P x 30% = P + P x 0,30 = 1P + 0,30P = 1,30P
augmentation de t% = 1,30P x t%
=> nouveau prix = 1,30P + 1,30P x t% = 1,45P
1,30 x (1 + t%) P = 1,45P
1,30 x (1 + t%) = 1,45
1 + t% = 1,45 / 1,30
t% = 1,115 - 1 = 0,115 soit 11,5 %