The hand of a clock rotates a full 360°, let's say 12 o'clock is 0°/360°. The hour hand for this example is at 3, it moved 90° and the minute hand marks 20 minutes meaning it's positioned on the 2. From 12 to 2 the minute hand has moved 60°. 90-60= 30. Therefore 3:20 forms a 30° angle.
