Grades 1-2 Video Solutions 2021-video 2021 1-2/17

Video Transcription

Problem number 17. Mara built the square shown by using four of the following five shapes. Which shape was not used? A, B, C, D, and E.  Before we get started, I have a note about this problem.  If you have an older printed version of this problem, you will notice that the stars and answers A and C are somewhat rotated.  This is because after the problem was published, it was discovered that even though Dojo Problem wanted you to think about the shapes that were there,  if you rotate the pieces, the stars would end up at different angles. So we will go with the stars as shown here in this version.  To start, you might want to check each of the pieces and see if it cannot be found in the board. If we look at piece A, we would rotate it and we can see that it's right here.  Piece B of the three diamonds can be found right here. Piece C could be either here or here. Piece D would be right here. And piece E with three arrows can be found here.  So just looking as to which of the pieces couldn't be found in the board does not give us the answer.  So we will need to figure out which of the four pieces were actually put together to make the square.  Piece E is the only one that has arrows in it, so it's pretty obvious that it was used and it was right here.  Piece A rotated would be here. Piece B would be the one right here. And that would leave piece C here. So if that's correct, then piece D is the one that was not used.  Just double-check. If we did use piece D, it would be right here. We have to use piece E, so this is taken up. And then this would be taken up.  And we would be left with these two shapes. A straight line of three pieces up here, two stars and a diamond. And a square of two circles and two stars.  These two shapes are not ones that were used. So if we used piece D, we would need some different shapes. So piece D is the one that Mara did not use.  Let's take a look at an animation that will help us see this in a little bit of a different way.  We see the shapes A, C, B, and E in this image. Shape D was not used.

Video Summary

The problem involves identifying which of five shapes (A, B, C, D, E) was not used to construct a square. After examining each shape's placement, the solution identifies that pieces A, B, C, and E were used. Piece D was not used in the construction, as its use would require additional shapes not present. The conclusion is confirmed with a visual demonstration.