Video: Using Images to Determine Whether Two Addition Expressions Are Equal

Madison has drawn this picture to show that 17 is an odd number. Her teacher asks her to complete the addition sentence that shows that 17 is odd. _ + _ + 1 = 17. She knows that she needs to write the same number in both boxes. What number is this?

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Video Transcript

Madison has drawn this picture to show that 17 is an odd number. Her teacher asks her to complete the addition sentence that shows that 17 is odd. What plus what plus one equal 17. She knows that she needs to write the same number in both boxes. What number is this?

The question is asking us to prove that 17 is an odd number. To do this, Madison’s teacher has asked her to complete the addition sentence. Which two numbers can we add together and then add one to to make 17? We could start by taking away one from 17, which is 16. 16 plus one is 17.

Because we know that Madison has to write the same number in both boxes, we could divide 16 by two. We’re dividing 16 into two equal groups. This helps us to see that eight plus eight plus one equals 17. 16 divided by two is eight, so two lots of eight, or eight plus eight, is 16. Plus one equals 17. So, the number that Madison needs to write in both boxes is the number eight.

We know that all even numbers can be found using doubles, and odd numbers are doubles plus one. So, double eight, which is 16, makes us an even number. Double eight plus one gives us the odd number 17.

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