A company imports components and pays in Euros. On a particular day in 2011; they found that the price of one component, in euros, was 10% less than it was when they bought it in 2009.

The exchange rate had also changed over two years in reference to when they completed the transaction in 2009:

a, 2009, 1E=£1

b, 2010, 1E = £0.95

c, 2011, 1E = £0.90

Find a percentage change in £ of the component in question between day a in 2009 and day c in 2011

Right, there is obviously a 10% deduction in the exchange rate over the two years, but really struggling how to incorporate this into the initial price deduction?! Would it involve using P = M(1-r%)^n ?

Any help would be greatly appreciated!