The total length of a measurement from a U.S. customary scaled drawing of 1/8 inch is 3.5 inches. What is the actual length?

Step one:

Convert the scale (1/8 inch) into a decimal format.

1/8 inch scale is 1 divided by 8 = 0.125 inches

Step two:

Determine the measurement on the scale drawing using a ruler. In this example our measurement is 3.5 inches.

Step three:

Divide the measurement by the scale decimal value. In other words, how many 0.125 units go into the measured length?

3.5 / 0.125 = 28 feet ; 8.53

The total length of a measurement from a metric (SI) scaled drawing of 1:50 is 100 mm. What is the actual length?

Step one:

Multiply 100 mm times the scale unit, 50.

100 * 50 = 5000 mm ; 5 meters