Number Detectives Slides
Math Mission • Grade 1-2
Numbers Up to 100
Case File #100
Number Detectives
Cracking the 2-digit code with Tens and Ones!
Count Tens
Group by 10s quickly
Add Ones
Count the extras
Say the Name
Read every number aloud
1
Detective Warm-Up: Quick Count!
Which way is faster?
Counting by Ones...
Counting every single dot one by one takes a long time!
1
2
3
4
...
20
Slow and easy to lose count!
Grouping by TENS!
Bundle into packs of 10 for super speed!
10
1 Ten
10
1 Ten
= 20!
Super fast and super accurate!
Detective Rule: 10 Ones snap together to make 1 TEN Rod!
2
Our Detective Tools: Base Ten Blocks
Rods & Units
THE TEN ROD
1 Rod
= 1 Group of 10
Value = 10
Whenever you see a tall blue rod, count “10”!
THE ONE UNIT
1
1 Unit
= 1 Single Cube
Value = 1
Whenever you see single cubes, count by “1s”!
3 Rods = 30 • 5 Rods = 50 • 7 Rods = 70 • 9 Rods = 90
3
The Place Value House
Every Digit Has a Home!
Let’s build the number 34!
TENS
3
3 Tens = 30
ONES
4
4 Ones = 4
30 + 4 = 34 (“Thirty-Four”)
Tens are on the LEFT • Ones are on the RIGHT!
4
Case #1: What’s My Number?
Class Clue Hunt
Inspect the Evidence
5 Tens
6 Ones
Step 1: Count Tens
5 tens = 50
Step 2: Count Ones
6 ones = 6
Step 3: Combine & Read!
56
“Fifty-Six”
Say it together: “Fifty-six has 5 tens and 6 ones!”
!
Detective Trap: Order Matters!
Don’t Get Tricked!
Are 24 and 42 the same number?
24
“Twenty-Four”
2 Tens (20)
4 Ones (4)
42
“Forty-Two”
4 Tens (40)
2 Ones (2)
NO! The position of the digit changes its value completely! 42 is much bigger than 24!
5
Mystery Number Challenge
Can You Solve It?
CLUES FOR SECRET AGENTS:
1
I have 7 tens in my tens place.
2
I have 3 ones in my ones place.
3
Expanded form: 70 + 3 = ?
On the count of 3, whisper the secret number!
73 (“Seventy-Three”)
6
Read & Say Aloud!
Reading 2-Digit Words
48
“Forty-Eight”
4 tens + 8 ones (40 + 8)
65
“Sixty-Five”
6 tens + 5 ones (60 + 5)
81
“Eighty-One”
8 tens + 1 one (80 + 1)
90
“Ninety”
9 tens + 0 ones (90 + 0)
Reading Tip: Say the tens name first, then add the ones! (e.g., “Forty” → “Eight”)
Mission Accomplished!
You Are Official Place Value Detectives!
Tens Left
Tens tell you how many bundles of 10.
Ones Right
Ones tell you how many extra single units.
Read & Write
Combine them to name any number to 100!
Ready for independent practice and mystery number games!
Great job, Number Detectives! • Case Closed!
