another related number Q

[irene]

Hi

Will really appreciate if anyone can explain this:

11 (13) 5; 9 (7) 6; 13 (?) 7.


Answer: 13

Thanks to all.

I

[Ambridge]

Ooh, good at these now....it's only taken two years!!


11 - 5 = 6 x 2 = 12 + 1 = 13

9 - 6 = 3 x 2 = 6 + 1 = 7

13 - 7 = 6 x 2 = 12 + 1 = 13


Ambridge x

[irene]

Wow. Thanks!