There are 100 winning tickets and 8000000 tickets so the probability of any one ticket would be [tex]\frac{100}{80000000}=0.00000125. If you buy 1000 tickets your probability of winnng a prize is or 0.125%. If the total value of all the 100 prizes is £1000000 (not euros?) then your "expected return" is (0.00125)(1000000)= £1250. Of course, The cost of each ticket will be more than £1.25 because the people setting up the raffle are not going to use money.