Changing a Scale

Question 1 • FL-1205040-M/J Grade 7 Mathematics B -GF

Which steps should be followed to use a scale drawing and a new scale to find the new length of a soccer field?

Answer

Add the numerator of the new scale to the old length to get the new length.

Subtract the new length from the old length to find the difference in lengths.

Write a proportion using the new scale as the first ratio. Set the first ratio equal to the ratio of the length of the original field compared to a variable that represents the new length of the field. Solve the proportion to find the new length of the field.

Write a ratio comparing the scale drawing length to the actual length of the field, and simplify.

Explanation

A scale drawing relates a drawing length to an actual length, so changing the scale requires setting up a proportion. Use the new scale as one ratio and the original field length compared with the unknown new field length as the other ratio, then solve for the unknown. Adding or subtracting lengths does not account for the proportional relationship, and simply simplifying the old scale ratio does not find the new length.

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