What number goes in the gray square?
A+B=8
X-Y=6
A+X=13
B+Y=8
2A+2B+2X=35
Which means A+B+X=17.5
A+B=8 so A+B+X= 17.5 8+C=17.5
X=17.5-8=9.5
We also know that
so A=13–9.5=3.5
A+B=8 B=8–3.5=4.5
B+Y=8 Y=8–4.5=3.5
So A=3.5 B=4.5 X=9.5 Y=3.5
