Nine numbers are taken from calender as shown
14 15 16
21 22 23
28 29 30
If the sum of all given numbers is S, then the value of S9 equals to
22
If sum of all the number is S, then the value of S9 is equal to middle number which is equal to 22.
Alternatively, It can be verified
x - 8 x - 7 x - 6
x - 1 x x + 1
x + 6 x + 7 x + 8
adding all we get sum as 9x and 9x9=x
which is the middle number.