More problems again...

when ever i try to do a percentage sum it puts 99 infront of it. e.g

.........A.................B
5| Month...........| January
6| Scheduled......| 100
7| Arrived..........| 25
8| Not Arrived....| 75
9| Percent.........| 9925.00%

the sum i am doing is =SUM(B6-B8%), this is so i can see the percentage of people turning up. really bugging me.