Present value of annuity cash flow

The five year annuity factor give the total factor for time 1 to 5. In scenario 1, since the amounts are at the start of each year, they are from 0 to 4. (time 0 is the start of the first year, time 1 is the start of the second year, and so on). The PV of an amount at time 0 is the same figure. The PV for flows from 1 to 4 is found by multiplying by the 4 year annuity factor. In scenario 2, the 5 year annuity factor gives the total for time 1 to 5. Since we only want the total for times 2 to 5, we subtract the discount factor for time 1. I do suggest that you watch the free Paper F2 lectures on discounting, because this is all revision from Paper F2.