Can someone help with F6?

ok, i am going through the practice and revision kit for F6 (tax) and i want to ask a quesiton about Question 29 – Jimmy.

Can someone explain why Jimmy has the full nil rate band of £325,000 available to him for his cash gift of £800,000 to a trust?

The part before it says that he made a cash gift to his grandson of £50,000 for his wedding. now, he gets to deduct his annual exemption from the 2 prior years (£6,000) and the wedding allowance (£2500) – so in fact his PET is only £41,500 (50,000-6,000-2,500).
Now, that is all swallowed up by his nil rate band – so there is nothing to pay as his nil rate is £325,000 and the PET is only £41,500.

when it comes to the part about the £800,000 gift to a trust (which he pays the IHT) why does he get to use £325,000 at nil rate and then £475,000 x 20/80 ? i thought that as there was a gift within the last 7 years (the £41,500 from above) then this would get taken away from his nil rate band.

i worked it out as £325,000 less £41,500 = new nil rate band of £283,500, and then the remainder (£516,500) at 20/80.

anyone?