Lesson 3.3 · Counting to 100
Counting by tens to 100
Counting to 100 one by one takes a long time. There is a faster way: count by tens!
Say the tens
When you count by tens, you say one number for each group of 10.
| 10 | 20 | 30 | 40 | 50 |
|---|---|---|---|---|
| ten | twenty | thirty | forty | fifty |
| 60 | 70 | 80 | 90 | 100 |
|---|---|---|---|---|
| sixty | seventy | eighty | ninety | one hundred |
Look at the numbers. Each one ends in 0. The first digit tells how many tens: 30 is 3 tens. 70 is 7 tens.
Counting by tens
Each full row of 10 gets one number: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. Ten tens make one hundred.
Worked example: Rows of beads
Each row has 10 beads. How many beads?
🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵
🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵
🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵 🔵
Count one number for each row: ten, twenty, thirty. There are 30 beads.
Worked example: Fingers in a class
Five kids hold up both hands. Each kid shows 10 fingers. How many fingers?
✋✋ ✋✋ ✋✋ ✋✋ ✋✋
Count by tens, one for each kid: ten, twenty, thirty, forty, fifty. There are 50 fingers.
Worked example: What comes next?
Fill in the blank: 60, 70, 80, ___
Count by tens: sixty, seventy, eighty, ninety. The answer is 90.
Common mistake
After 90 comes 100, not "ten-ty." And it is forty, not "four-ty."
Practice
Each row has 10 stars. How many stars?
⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐
⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐ ⭐
Type a number.
What comes next? 10, 20, 30, ___
Type a number.
Each row has 10 dots. How many dots?
🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣
🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣
🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣
🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣 🟣
Type a number.
What number is missing? 40, 50, ___, 70
Type a number.
What comes right after 90 when you count by tens?
Seven kids each hold up 10 fingers. How many fingers is that?
Type a number.
Which list counts by tens?