You start off with 100% of the total
If it is Decreased by 5% it goes Down by 5% so you end up with (100-5)% = 95%
You can either find 5% and take it off the original amount OR you can just find 95% to start with
If it is Increased by 5% it goes up by 5% so you end up with (100+5)% = 105%
You can either find 5% and add it to the original amount OR you can just find 105% to start with.
So just remember D is for Decrease and for Down