RE: Maths Brain Teasers 50:: Can You Complete the Circle Puzzle?

There are actually 2 patterns. You either subtract the 2 smaller from the 2 bigger numbers in the circle and you will get the center number, in this case the solution is 15.
But you can also subtract the lower right and upper left numbers from the other 2, in this case the solution is 9.
To me it inconclusive which is the right pattern, in the first 2 circles the the lower right and upper left numbers happened to be also the 2 biggest numbers.