Florida B.E.S.T. MA.8.GR.2.2
The Standard
Given a preimage and image generated by a single dilation, identify the scale factor that describes the relationship.
Florida B.E.S.T. Standards for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students match corresponding lengths in the original figure and its image. They divide an image length by the matching preimage length and interpret factors above or below 1.
What Mastery Looks Like
- A student can find the same scale factor from any pair of corresponding lengths, including fractional factors. They can tell whether the dilation enlarges or reduces the figure and justify the ratio used.
Common Misconceptions
- Students often reverse the ratio and report the reciprocal scale factor. They may subtract lengths instead of dividing, match noncorresponding sides, or assume every dilation enlarges a figure.
How to Assess It
- Exit ticket: A segment of length 8 is dilated to a segment of length 12. Find the scale factor and write the ratio you used.
Lesson moves
Ways to Teach It
Give pairs of cutout rectangles; students measure matching sides, calculate image length divided by preimage length, and label each dilation.
Ask, "Why is the scale factor 2.5 when a 4-unit side becomes 10 units, and not 0.4?"
Play Scale Factor Match with cards showing figure pairs, side lengths, and factors; students build correct sets and explain one match.
Compare an original photo and a resized print, then use their widths to calculate the printer's scale factor.
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Related Standards
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Given a preimage and image, describe the transformation and represent the transformation algebraically using coordinates.
- MA.8.GR.2.1
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- MA.912.GR.2.8
Apply an appropriate transformation to map one figure onto another to justify that the two figures are similar.
- MA.912.GR.4.3
Extend previous understanding of scale drawings and scale factors to determine how dilations affect the area of two-dimensional figures and the surface area or ...
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