Third hardest question on a hospital IQ test(Fill the blank) 
Place the numbers 1 through 9 in the available input boxes so that the
  results of performing the mathematical operations in any row and
  column (from left to right and top to bottom) always equals 13.
\begin{bmatrix}\square&+&\square&-&\square\\
 -& &+& &\times\\ \square&\times&\square&+&\square\\
 +&&-&&+\\ \square&\times&\square&-&\square\\ \end{bmatrix}

It takes me an hour to solve this. Do you have an easy way to solve this? Let's explore.
Original image here.

Label spaces A through I.
A+B, B+E,A+G are all at least 14.  So A,B,E, and G are all greater than or equal to 5.
D x E must be less than 13 and E is 5 or more so D = 1 or 2.
If D=2 then E=5.  If E = 5 then B+5-H=13 so B=9, H=1.  So Gx1 -I =13 is impossible.
So D isn't 2.  So D=1.  So E+F = 13,  so F is at least 4.  C x F +I = 13 but F is at least 4 and I is at least 3 and C is at least 2.  
If C is at least 3 then CxD+I is at least 14 so C is at most 2 and at least 2.  So C is 2 and I is at least 3.
2x F + I =13 and F is at least 4 so we have either 2x4 + 5.  Or 2x5 +3.
If F=4, I=5, E=9.  GxH = 18 and neither G or H is 9 so G and H are 3 and 6.  And G is at least 5 so G = 6, H =3 and B+9-3=13 so B=7.  That leaves A =8.  And that works as A+7-2=13 and A-1+6=13.
That's a solution.
any other solution would have F=5 and I =3 and E=8.
So A+B=11, GxH= 16, A+G=12, B-H=5. 1,2,3 are assigned so G and H are at least 4, so G xH =16 is impossible.
So only solution is
A=8,B=7,C=2,D=1,E=9,F=4,G=6,H=3,I=5.
