It mats with 3 number you pair them up have to add or minus them from each other and then write the anwser took - sorry I dont think I explained it very well though have a look at it and you'll figure it out!!
Basically, you add the numbers on the top line together and then put the sum of those numbers into the second line and do whatever the calculation is for the answer:
Eg. 2 + 8 - 3
O+O
A
With this one you would do 2+8 and mentally put that number into the left circle and then do 8-3 and put that number in the right circle.
The sum you're left with then is 10 + 5 so 15 is the answer.
for cakeboy...sussed it b4 your answer but your answer does explain it very well.i can do it now but not every time.hope other people read your answer b4 thinking like me.god i'm dumb.thanks once again for brill people with all the answers on his site.