Proportions and Scale Factor

scale and scale factor

Scale drawings and models

To solve scale problems, use a proportion!

Set up a Scale proportion

• write the word ratio of units

• make the first ratio the scale

• put the numbers from the problem in the appropriate place in the proportion

Multiple Choice

A scale drawing has a scale of 1cm:2ft. What is the actual width of a pool if it is 6cm on the drawing?

• 3ft

• 6ft

• 12ft

To find the scale

• write the word ratio

• put 1 over x for the scale ratio

• put the numbers from the word problem in the second ratio

• solve the proportion algebraically

Multiple Choice

A model ship is 30cm long and the actual ship is 150m long. What is the scale?

• 1cm:5m

• 1cm:3m

• 1cm:50m

• 1cm:150m

To find the scale factor

• use conversions to write the scale with matching units (use a proportion)

• the scale factor is the ratio written without units

Multiple Choice

The scale in an advertisement is 1in:6ft. What is the scale factor?

• 1:72

• 1:6

• 1:36

• 1:12