(i) Probability of getting two heads = 0.5*0.5 = 0.25 (Here we multiply the probability of getting a head by the probability of getting a head)
(ii) Probability of getting at least one head = 0.5*0.5 + 0.5*0.5 + 0.5*0.5 = 0.75 (Here we add the probability of getting a head and a head to the probability of getting a head and then a tail and then add the probability of getting a tail and then a head) The second way to do this is to subtract the probability of not getting any heads (ie. getting a tail and a tail) from 1: 1 - 0.5*0.5 = 1 - 0.25 = 0.75
If there are 20 and stickers are sold in 15 sheets, then you got to work backwards. take the answer and multiply it by the amount of sheets. For example: 4 times 15 is 60, 60 divided by 20 is 3. No leftover numbers.
