Finding Correct Numbers For The Boxes

How boxes are placed?

Let's assume a, b, c and d are the correct numbers in the boxes.

So, 4 equations that we get are,

a + b = 8     .....(1)

c - d = 6     .....(2)

a + c = 13   .....(3)

b + d = 8    .....(4)

Subtracting (1) from (3) gives,

c - b =  5     .....(5)

Adding (2) to (4),

c + b = 14    .....(6)

Adding (5) and (6) gives,

2c = 19

c = 9.5

Putting c = 9.5 in (2),

9.5 - d = 6

Hence, d = 3.5

Putting d =3.5 in (4),

b + 3.5 = 8

b = 4.5

Putting b = 4.5 in (1),

a + 4.5 = 8

a = 3.5

So to conclude, a = 3.5, b = 4.5, c = 9.5 and d = 3.5.