Video: Determining the Measure of an Angle Using the Protractor

Jacob and Mia are measuring angles. Which of the two is correct?

01:25

Video Transcript

Jacob and Mia are measuring angles. Which of the two is correct, Jacob or Mia? Jacob says, “The measure of the angle is 70 degrees.” And Mia says, “The measure of the angle is 110 degrees.”

Let’s look more closely at the protractors and see who’s correct. Both children are measuring the same angle, so we know that one of them has made a mistake. It looks like Jacob started measuring here at zero. 10, 20, 30, 40, 50, 60, 70. This is why he thinks the measure of the angle is 70 degrees. But we’re not trying to find the measure of this angle. It looks like Jacob started in the wrong place. There are two scales on our protractor. It looks like Mia started at zero on this scale, on the opposite side of the protractor. And she’s counted round to 110. 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110. The measure of the given angle is 110 degrees. So, Mia is correct.

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