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WordPress.com sent me a report on this blog. It was viewed 160,000 times in 2011. Thanks to everybody for your participation—and congratulations to Brian Cohen for posting the largest number of comments!

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Good Morning, Bill,

I have a clarification question about some measurement & data terminology and I wasn’t sure exactly where to post. In 2nd grade, line plots are introduced as a data representation. In 6th grade, the standards refer to dot plots. How are these alike and how are they different? We have typically seen those terms used to mean the same thing.

Thank you,

Julie

Maybe you’ve already seen this by now . . . Here’s what the CCSS glossary says:

Line plot. A method of visually displaying a distribution of data values where

each data value is shown as a dot or mark above a number line. Also known as a

dot plot.

OT:

Bill,

The definition of dilations provided in the CC document is somewhat hard to parse, but seems to imply that only positive scale factors are admitted (no inversion). It does not change what figures are considered similar, but that makes a difference in what combinations of transformations can map one figure onto another, specifically, you never “need” reflections if negative scale factors are included. Is my reading of “positive scale factors only” correct?

Dilation. A transformation that moves each point along the ray through the

point emanating from a fixed center, and multiplies distances from the center by

a common scale factor.

Thank you,

Alexei

Alexei, this is the correct interpretation, although I agree that mathematically it would be fine to have negative scale factors. But perhaps this would be a bit confusing to the students, and its better to separate out the reflections as a distinct type of transformation.