Yes, what he said. There are 9 sets of numbers. Each uses the same four digits in a second set except the first one, 6394. I tried adding the 4 digits together and thought that was going to be the answer until I got to the last number. Up until that point, the only number with an "odd' sum was the 7th number. But then the 9th matched it, obviously.
RE: Maths Brain Teasers 40:: Can You Find the ODD One Out???