Mystery Number Slides Case File: Place Value
Mystery Number Detectives
Using Ten-Sticks and Ones to Crack the Code!
Yellow = Tens
Pink = Ones
Warm-up: Flash Math!
Look Fast!
?
What number did you see?
Detective Training Video
We're going to watch a special video about teen numbers.
Look for Yellow & Pink!
Embedded media
STOP AT 2:11
Khan Academy: Teens as sums with 10
Prediction Break!
The narrator left us a challenge! Use your Prediction Slips to complete the pattern.
How do we write 16?
How about 17, 18, and 19?
1 6 = 10 +
?
The Mystery Bag Case
Level: Master Detective
1
Check Label
What is the secret teen number on the bag?
2
Find Missing
There is 1 ten-stick inside. How many ones are missing?
3
Solve Case
Add the cubes, then dump the bag to check your total!
Detective Journal
Why is the number 11 special?
1 Ten
1 One
Prediction Slips Worksheet Teacher Note:
Cut along the dashed lines. Each student needs one slip for the video pause point at 2:11.
Prediction Slip
Case #016-19
Name:
The Missing Pattern:
16 = 10 +
17 = 10 +
18 = 10 +
19 = 10 +
Prediction Slip
Case #016-19
Name:
The Missing Pattern:
16 = 10 +
17 = 10 +
18 = 10 +
19 = 10 +
Prediction Slip
Case #016-19
Name:
The Missing Pattern:
16 = 10 +
17 = 10 +
18 = 10 +
19 = 10 +
Prediction Slip
Case #016-19
Name:
The Missing Pattern:
16 = 10 +
17 = 10 +
18 = 10 +
19 = 10 +
Mystery Bag Log Worksheet Mystery Bag Case Log
Detective Unit: Teen Number Division
Detective Name
Date
Mission Briefing
1. Look at the Label on your bag. Write it in the circle.10-Stick that is already inside.ones you need to add to match the label!
Bag Label
?
10
How many ones?
=
Total
Bag Label
?
10
How many ones?
=
Total
Bag Label
?
10
How many ones?
=
Total
Evidence Check: Dump out your bag and count. Did you get the right total?
Mystery Number Teacher Guide Confidential: Teacher Eyes Only
Case File: Mystery Numbers
1st Grade • Place Value • Missing Addends
REF: MATH-G1-PV-001
Mission Objectives
Identify teen numbers as 10 + n.
Solve for missing ones in a teen number decomposition.
Recognize visual patterns in base-ten representations (ten-sticks).
1
Warm-up: Rapid Fire (5 min)
Hold up a physical 10-stick. Rapidly add cubes (start with 3). Ask the class to shout out the total. Repeat with different teen numbers to build fluency.
2
Evidence Analysis (10 min)
Play the Khan Academy video. Use the following critical pause points:
0:37
"What pattern do you notice in the second column?"
1:21
"Why is 11 made of two 1s? Do they mean the same thing?"
2:11
MANDATORY PAUSE: Hand out Prediction Slips.
3
Mystery Bags Activity (15 min)
Prepare brown bags with a teen number label (11-19). Place exactly one 10-stick inside each bag.
Students must determine how many ones are missing, draw/record it, then add the cubes to verify.
Gear Checklist
Brown Paper Bags (11-19)
Connecting Cubes (10-sticks & ones)
Prediction Slips
Case Log Worksheets
Detective Journals
Red Flags
The "Face Value" Trap: Students may see "12" as just 1 + 2. Emphasize that the '1' in the tens place is actually a giant 10 wearing a '1' costume.
Level Up
Once students finish their cases, have them create their own Mystery Bag for a partner. They must choose a teen number and put ONLY the ten-stick inside for the partner to solve.
Keyword 1 Tens Place
Keyword 2 Ones Place
Keyword 3 Pattern
Keyword 4 Decomposition
Mystery Bag Labels Resource Teacher Setup:
Cut out these labels and tape them to the front of brown paper bags. Place one 10-stick of connecting cubes inside each bag before starting the activity.
Case Label
Mystery Bag
11
Case Label
Mystery Bag
12
Case Label
Mystery Bag
13
Case Label
Mystery Bag
14
Case Label
Mystery Bag
15
Case Label
Mystery Bag
16
Case Label
Mystery Bag
17
Case Label
Mystery Bag
18
Case Label
Mystery Bag
19
Detective Journal Page Detective Journal
Case File #011: The Special Case of 11
Detective ID
1. Why is the number 11 special? What did you discover about it today?
2. Draw what 11 looks like using a ten-stick and ones.
Evidence Drawing Area
Case Solved?
Yes!
I need more clues.
Mystery Number Answer Key Detective Solution Key
Teacher Reference • Mystery Number Detectives
KEY-PV-01
Video Prediction Slips
Solutions for the mandatory pause point at 2:11.
16 = 10 + ___ 6
17 = 10 + ___ 7
18 = 10 + ___ 8
19 = 10 + ___ 9
Teaching Tip
The narrator explicitly shows these answers after the pause. Use this key to check students' slips before resuming the video for maximum impact.
Mystery Bag Master List
Each bag contains exactly ONE 10-stick.
Bag Label Ones Needed 11 1 12 2 13 3 14 4 15 5 16 6 17 7 18 8 19 9
Reflection: Why is 11 Special?
Look for answers that mention:
It is made of two "1"s, but they mean different things.
The first "1" is a 10 (ten-stick).
The second "1" is just a single one (cube).
In their drawing: One long stick (10 units) and one small cube.
