# What's the missing number?

$$\begin{array}{ccc}6&7&4\\ 4&11&14\\ 13&2&11\\ 6&8&1\\ 15&3&?\end{array}$$

Own attempt at building a puzzle, find the missing number.

if we sum the numbers in an X Formation, they turn out to be equal. Like: $$\begin{array}{cccccc}6&&7&&4\\& + &&& \\4&&11&&14\\&&& + & \\13&&2&&11 & =28\\\\6&&8&&1\\\\15&&3&&?\end{array}$$- $$\begin{array}{cccccc}&6&&7&&4\\&&&&+& \\&4&&11&&14\\&&+&&&\\28 = &13&&2&&11\\\\&6&&8&&1\\\\&15&&3&&?\end{array}$$ and if we use the same rule on the lower X formation like this $$\begin{array}{cccccc}&6&&7&&4\\\\&4&&11&&14\\\\&13&&2&&11&\\&&&&+&\\&6&&8&&1\\&&+&&&\\34 =&15&&3&&?\end{array}$$- $$\begin{array}{cccccc}6&&7&&4\\\\4&&11&&14\\\\13&&2&&11&\\&+&&&\\6&&8&&1\\&&&+&\\15&&3&&?& = 34 \end{array}$$ so "?" should be 13 to maintain this rule
• Doesn't seem to hold in general: for the X in the center $4+2+1 \neq 6+2+14$ – elias Jul 12 at 10:27