Hi,
Did you try it? This is the block of 9 numbers that I tried.
The average of the 4 corner numbers is
(9 + 11 + 23 + 25)/4 = 68/4 = 17
and 17 is the middle number.
Why does it work?
Spread the 3 rows of the calendar into one row.
8 
9 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
Can you see now why 17 is the average of the 4 corner numbers?
Penny
