Skill: Find the missing half

A whole split into 2 equal parts has 2 halves. If you can see one half, the missing half must be the other part that is the same size and shape.

Example:

A rectangle is split into 2 equal parts. The left half is shaded. What is the missing half?

+-------+-------+
| shaded|       |
|  half |   ?   |
+-------+-------+

Step 1: Look at the whole rectangle. It is split into 2 equal parts.

Step 2: One part is already shown: the shaded half.

Step 3: The missing half is the blank part. It must be the same size as the shaded part.

+-------+-------+
| shaded| blank |
|  half |  half |
+-------+-------+

So, the blank part is the other half. Together, the two halves make the whole rectangle:

$$\text{half}+\text{half}=\text{whole}$$