An example of solving a number line mystery by process of elimination. red x's indicate values that have been eliminated and a blue circle indicates the solution.Summary:

After students understand how to solve and illustrate Fraction Number Line Mysteries they write their own Fraction Number Line Mystery like this:

  1. I am a point on a number line that starts with 0 and ends at 1.
  2. The number line is cut into 4 equal pieces.
  3. I am larger than 1/2 or 2/4.
  4. I am smaller than 4/4.
  5. My denominator is a 4.
  6. Which number am I? Answer: 3/4
Then students create a Scratch activity that solves and illustrates their mystery. They use their own voices to record the clues for their mystery.


Programing Skills with Scratch:

  • Open, remix, and save a Scratch activity
  • Duplicate a backdrop and change its looks using paint drawing tools
  • Switch backdrops
  • Add recordings of their voice to a Scratch activity Scratch blocks used: (wait, switch backdrop to, play sound recording __until done, glide _ sec to x:_ y:_)


  1. Students should be familiar with Fraction Number Line Mysteries and with how to illustrate them.
  2. Use the Math Background Knowledge for sample mysteries.An example of solving a number line mystery by process of elimination. Red x's indicate values that have been eliminated and a blue circle indicates the solution. Below the number line the equivalent fractions 1/2 and 2/4 as well as 1 and 4/4 are illustrated.
  3. When students are comfortable solving mysteries and can illustrate the mysteries with your guidance, pass out the My Fraction Number Line Mysteries. With partners or in small groups, allow time for students to complete the three mysteries together.
  4. Review the 3 mysteries. Together do the, ??? Look for patterns in Fraction Number Line Mysteries, part of the worksheet. Students should notice:
    • Clue #1 gives the starting and ending points on the number line.
    • Clue #2 tells how many equal pieces into which the number line is cut.
    • The last line always asks, “Which number am I?”
    • The middle clues help eliminate possible answers. There should only be one possible answer.
  5. Pass out the My Mystery Planning Page. Decide if you want students to work alone or with partners. Allow time for students to create and illustrate their own Fraction Number Line Mysteries using the worksheet. Note, the worksheet allows up to 6 clues.
  6. After you have approved all of the students mysteries, show students how the Scratch activity was created. Open the link to the My Fraction Number Line Mystery Scratch activity (student version)
  7. Be sure students know how to duplicate and change the look of a backdrop.A screenshot of the menu showing that the stage sprite is above the new backdrop menu.
    1. Click the Stage sprite below the stage.
    2. Click the Backdrops tab shown near the top of the screen.A screenshot of the menu tabs showing that the backdrops tab is the middle tab located between the Scripts and Sounds tabs.
    3. Right click backdrop1, then select duplicate.
    4. A new called backdrop2 will appear in the column below backdrop1.
    5. Click backdrop2. Use the paint drawing tools to change its look by adding lines that show how the number line should be divided. This information was given in Clue #2.
    6. After you have made all the changes you need for the Clue #2, right click backdrop2 and select duplicate.
    7. A new backdrop3 will appear below backdrop2. Change the way it looks by adding illustrations with the paint drawing tools for Clue #3.
    8. Continue duplicating each backdrop and changing the way the next backdrop looks until you have enough backdrops for all the clues in your mystery. There should be a backdrop that illustrates every clue. The clue number and the backdrop number should match.
  8. Information for teacher:

    In order to create straight horizontal or vertical line segments while using paint drawing tools, press and hold the shift key on the key board while drawing the segment. The segment will automatically align horizontally or vertically while the shift key is pressed.

  9. Be sure students know how to record their voices.
    1. Click the Sounds tab.A dialogue box indicating that a program is attempting to use the camera and microphone. The allow button is located in the bottom left of the dialogue box adjacent to the deny button.
    2. Click the microphone icon.
    3. Click the circle to start and stop recording your voice. While you are recording, the circle turns red.
    4. If asked, allow Scratch to access the camera and microphone of your computer.
    5. After you have recorded Clue #1 in recording1, you can listen to it by clicking the triangle.
    6. If you want to rerecord your voice, press the x shown by recording1 and start again.
    7. Do not start to record Clue #2 until you are happy with the way Clue #1 sounds.
    8. To record Clue #2, press the microphone icon and record your voice.
    9. Continue recording your voice for every clue. Be sure the recording number matches the clue number.A screenshot of the sounds tab. The sounds tab is the tab on the far right. The record new sound button is the second button from the left in the new sound menu between the choose sound from library and the upload sound from file buttons. You can remove sounds by selecting them in the left-hand column and clicking the x in the top right corner of the sound. The play and record buttons are located on the left and right hand sides respectively of the stop button located above the microphone volume slider.
  10. Be sure students know how to create a script for the backdrop.A screenshot showing that the stage sprite is above the new backdrop menu.
    1. Click the picture of the Stage sprite shown below the stage.
    2. Click the Scripts tab.
    3. Click the LOOKS category to find the switch backdrop to block.
    4. Click the SOUND category to find the play sound _ until done block.
    5. To create a script for the backdrop, drag and drop the blocks into the script area in the same way you create a script for any sprite.A screenshot of the scripts tab, located to the right of the backdrops and sounds tabs.
  11. Information for teacher:

    The backdrop sprite does not have any blocks from the MOTION category because a backdrop cannot move. If you click on the MOTION category it will say, “Stage selected: No motion blocks”.

  12. Encourage students to be careful with sequence. They may want to place the recording blocks before the change backdrop blocks in their scripts so that viewers of their activity will hear their clues before they see the pictures.
  13. Ask students which EVENTS block they will use to start their script.
  14. Allow time for students to open and remix the Scratch activity My Fraction Number Line Mystery Scratch activity (student version). The first backdrop for Clue #1 has already been created. The cat sprite has been deleted. It is ready for students to create the backdrops for each clue and to record their voices for each clue.
  15. Allow time for students to share their activities.


  • Ask students how they could add a sprite and use a glide _ sec to x:_ y:_ block to make the sprite move along the number line to the correct location when the answer is given.
  • Allow students to create and illustrate more than one mystery.


  • If students are having difficulties using the paint drawing tools to create the backdrops for each clue, make arrangements for older students to help your students with the paint drawing tools.
  • If students need additional help, create backdrops students can use. Then they can record their voices for each clue and sequence the blocks correctly for their mystery.

Unplugged Activity:

(Plan to allow several minutes on many days with these Unplugged Activities before beginning the Scratch activity.)

Common Core:

3.NF.A.1, 3.NF.A.2, 3.NF.A.2.A, 3.NF.A.2.B, 3.NF.A.3, 3.NF.A.3.A, 3.NF.A.3.B, 3.NF.A.3.C, 3.NF.A.3.D

CT/CS Standards:

CS-Write programs that accomplish specific goals, Use sequence in programs, Design and create content, Present information
CT-Decomposition, Pattern Recognition, Pattern generalization & abstraction

Champaign Unit 4 School DistrictKenwood Elementary School: bright stars, bright futures
College of Education at IllinoisUChicago STEM EducationNSF
These lessons were written by Judy Rocke based on lessons developed at Kenwood Elementary School in the Champaign Unit 4 school district. Funding was provided by the National Science Foundation under award number 1542828. These lessons are intended to be used alongside the EM-4 curriculum.

Lessons prepared as web documents in Summer 2017. Contact us for updated lesson plan materials.