Explain what a bar scale and a number scale are, the meaning of the scale 1:50, and calculate the actual length and distance of a desk.

• A bar scale is a graphic representation of the scale, usually a line segment divided into parts, with actual distances marked. It remains accurate even if the map or plan is resized.
• A number scale (or ratio scale) is expressed as a ratio (e.g., 1:50) or a fraction. It indicates that one unit on the map represents a certain number of units in reality. It becomes inaccurate if the map or plan is resized.

The meaning of the scale 1:50 is that 1 unit of measurement on the plan represents 50 of the same units of measurement in actual length. For example, 1 cm on the plan represents 50 cm in reality.

The length of the desk on the plan is 6 cm. The scale is 1:50.
To find the actual length, multiply the plan length by the scale factor.

Convert the actual length from centimeters to meters (since 1 m = 100 cm):

The actual length of the desk is $\boxed{3 \text{ m}}$.

The distance between the desks on the plan is 4 cm. The scale is 1:50.
To find the actual distance, multiply the plan distance by the scale factor.

Convert the actual distance from centimeters to meters (since 1 m = 100 cm):

The actual distance between the desks is $\boxed{2 \text{ m}}$.