You know how to count by tens (Counting by Tens): 10, 20, 30, 40, 50, 60, 70, 80, 90 … What comes next? 100! That is 10 tens.
Why it works
We bundle by tens again and again. 10 ones make 1 ten. 10 tens make 1 hundred. A hundred flat is exactly 10 ten-rods side by side, so it is the same amount, just packed into one piece. Bundling lets us count big piles quickly.
Worked example: Tens in 300
How many tens are in 300?
- Each hundred is 10 tens.
- 3 hundreds is $10 + 10 + 10 = 30$ tens.
Answer: 30 tens
Worked example: Hundreds with zeros
Write the number for 7 hundreds, 0 tens and 0 ones.
- Write 7 in the hundreds place.
- There are no tens or ones, so write 0 in both of those places.
- The number is 700, seven hundred.
Answer: 700
Worked example: More than 10 tens
What number is 12 tens?
- 10 of the tens make 1 hundred.
- 2 tens are left over: that is 20.
- $100 + 20 = 120$.
Answer: 120
Key idea
10 ones make 1 ten, and 10 tens make 1 hundred. The numbers 100, 200, 300, … 900 mean 1, 2, 3, … 9 hundreds, with 0 tens and 0 ones.
Common mistake
Thinking 300 has 3 tens. The 3 in 300 means 3 hundreds, and each hundred is 10 tens, so 300 has 30 tens. Check with money: 3 one-dollar bills are worth the same as 30 dimes.
Grown-up tip: Bundle straws or craft sticks with rubber bands: 10 singles in a bundle, then 10 bundles in a big bundle.