Chapter at a Glance
- Chapter: 1
- Strand: Foundations
- Difficulty: Level 1 of 5
- Builds on: Counting to 100 by ones and tens
Try This First
Try this short activity before reading the lesson.
> Get a cup of dry beans or a box of paper clips. Count out ten and put them in a pile. Make as many piles of ten as you can. Then count the piles: "ten, twenty, thirty..." and count the leftovers on by ones. Say the number you land on out loud.
Math Lab: Count on past one hundred
Predict first. You are counting beads and you reach $99$. Say the next three numbers in your head before you read on.
<div class="math-model"><p><strong>Counting on across 100.</strong></p><div class="model-bar"><span class="model-cell">99</span><span class="model-cell">100</span><span class="model-cell">101</span><span class="model-cell">102</span></div></div>
Model and solve. One more than $99$ is $100$. After $100$ the counting starts again, just like the numbers you already know: one hundred one, one hundred two. You write them $101$ and $102$.
Explain. Why is one hundred one written $101$ and not $1001$?
Your turn. Count on from $97$ to $103$.
Check after trying. $97, 98, 99, 100, 101, 102, 103$.
The Big Idea
Counting is a road, and every number is the next stop on it. After $99$ the road does not stop. The next stop is $100$, then $101$, $102$, and on to $120$. The numbers after one hundred sound like "one hundred and then a small number": one hundred one, one hundred two.
Writing a number past one hundred takes three digits, no more. One hundred fourteen is $114$: a $1$ for the hundred, then $14$. It is not $10014$. Say the hundred, then write the rest in the two places after it.
You can start counting anywhere on the road. Start at $87$ and keep walking: $88$, $89$, $90$, $91$. You do not have to go back to $1$ to know what comes after $89$.
For grown-ups. Counting past 100 is where a child first meets the pattern that every later number system repeats: the ones roll from 9 back to 0 and the tens tick up by one. Students count forward from any number, read and write numerals to 120, and say how many objects are in a group that big. Place value, the hundred chart and every two-digit sum stand on this.
Words to Know
- numeral: The written number, made of digits: $114$ is the numeral for "one hundred fourteen".
- count on: Start at a number and keep counting from there instead of starting at $1$. Counting on from $87$: $88, 89, 90$.
- decade number: A number that ends in $0$: $40$, $70$, $110$. The ones start again from $1$ after each decade number.
Outcomes and Milestones
- Students can: count forward from any number within 120, read and write numerals to 120, and count a group of up to 120 objects by tens and ones.
- Watch for: saying “one hundred, two hundred” after 100 instead of 101; writing one hundred fourteen as 10014.
- Ready when: they can start at 87 and count aloud to 120 without a chart, and write 109 and 113 from the spoken words.
Worked Examples and Your Turn
Study each example, then try the paired problem.
Example 1: Count on from the middle
Problem: Start at $66$ and count on to $75$.
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 400 100" width="400" height="100" role="img" aria-label="Number line from 65 to 76. Nine small hops go from 66 to 75, one number at a time." font-family="Source Sans 3" font-size="14"><line x1="10" y1="70" x2="390" y2="70" stroke="#333" stroke-width="1.5"/><polygon points="392,70 385,73.5 385,66.5" fill="#333" stroke="#333" stroke-width="1"/><polygon points="8,70 15,66.5 15,73.5" fill="#333" stroke="#333" stroke-width="1"/><line x1="22" y1="63" x2="22" y2="77" stroke="#333" stroke-width="1.5"/><text x="22" y="92" text-anchor="middle" font-size="13" fill="#333">65</text><line x1="54.4" y1="63" x2="54.4" y2="77" stroke="#333" stroke-width="1.5"/><text x="54.4" y="92" text-anchor="middle" font-size="13" fill="#333">66</text><line x1="86.7" y1="63" x2="86.7" y2="77" stroke="#333" stroke-width="1.5"/><text x="86.7" y="92" text-anchor="middle" font-size="13" fill="#333">67</text><line x1="119.1" y1="63" x2="119.1" y2="77" stroke="#333" stroke-width="1.5"/><text x="119.1" y="92" text-anchor="middle" font-size="13" fill="#333">68</text><line x1="151.5" y1="63" x2="151.5" y2="77" stroke="#333" stroke-width="1.5"/><text x="151.5" y="92" text-anchor="middle" font-size="13" fill="#333">69</text><line x1="183.8" y1="63" x2="183.8" y2="77" stroke="#333" stroke-width="1.5"/><text x="183.8" y="92" text-anchor="middle" font-size="13" fill="#333">70</text><line x1="216.2" y1="63" x2="216.2" y2="77" stroke="#333" stroke-width="1.5"/><text x="216.2" y="92" text-anchor="middle" font-size="13" fill="#333">71</text><line x1="248.5" y1="63" x2="248.5" y2="77" stroke="#333" stroke-width="1.5"/><text x="248.5" y="92" text-anchor="middle" font-size="13" fill="#333">72</text><line x1="280.9" y1="63" x2="280.9" y2="77" stroke="#333" stroke-width="1.5"/><text x="280.9" y="92" text-anchor="middle" font-size="13" fill="#333">73</text><line x1="313.3" y1="63" x2="313.3" y2="77" stroke="#333" stroke-width="1.5"/><text x="313.3" y="92" text-anchor="middle" font-size="13" fill="#333">74</text><line x1="345.6" y1="63" x2="345.6" y2="77" stroke="#333" stroke-width="1.5"/><text x="345.6" y="92" text-anchor="middle" font-size="13" fill="#333">75</text><line x1="378" y1="63" x2="378" y2="77" stroke="#333" stroke-width="1.5"/><text x="378" y="92" text-anchor="middle" font-size="13" fill="#333">76</text><path d="M54.4,70 Q70.5,52 86.7,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="86.7,70 78.4,66.7 84.4,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M86.7,70 Q102.9,52 119.1,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="119.1,70 110.8,66.7 116.7,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M119.1,70 Q135.3,52 151.5,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="151.5,70 143.1,66.7 149.1,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M151.5,70 Q167.6,52 183.8,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="183.8,70 175.5,66.7 181.4,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M183.8,70 Q200,52 216.2,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="216.2,70 207.9,66.7 213.8,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M216.2,70 Q232.4,52 248.5,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="248.5,70 240.2,66.7 246.2,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M248.5,70 Q264.7,52 280.9,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="280.9,70 272.6,66.7 278.5,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M280.9,70 Q297.1,52 313.3,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="313.3,70 304.9,66.7 310.9,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><path d="M313.3,70 Q329.5,52 345.6,70" fill="none" stroke="#e06666" stroke-width="2"/><polygon points="345.6,70 337.3,66.7 343.3,61.4" fill="#e06666" stroke="#e06666" stroke-width="1"/><circle cx="54.4" cy="70" r="5" fill="#e06666" stroke="#333" stroke-width="1"/><circle cx="345.6" cy="70" r="5" fill="#93c47d" stroke="#333" stroke-width="1"/></svg>
Solution:
- Say $66$, then the next number: $67$. Why: counting on means starting where you are, not at $1$.
- Keep going by ones: $68, 69$. The next number after a $9$ in the ones is the next decade number, $70$.
- Carry on: $71, 72, 73, 74, 75$. Stop at $75$.
Answer: $66, 67, 68, 69, 70, 71, 72, 73, 74, 75$.
> Notice: Every time the ones reach $9$, the next number ends in $0$ and the tens go up by one.
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 360 90" width="360" height="90" role="img" aria-label="Number line from 57 to 64. A red dot marks 58, where you start. An empty ring marks 63, where you stop." font-family="Source Sans 3" font-size="14"><line x1="10" y1="50" x2="350" y2="50" stroke="#333" stroke-width="1.5"/><polygon points="352,50 345,53.5 345,46.5" fill="#333" stroke="#333" stroke-width="1"/><polygon points="8,50 15,46.5 15,53.5" fill="#333" stroke="#333" stroke-width="1"/><line x1="22" y1="43" x2="22" y2="57" stroke="#333" stroke-width="1.5"/><text x="22" y="72" text-anchor="middle" font-size="13" fill="#333">57</text><line x1="67.1" y1="43" x2="67.1" y2="57" stroke="#333" stroke-width="1.5"/><text x="67.1" y="72" text-anchor="middle" font-size="13" fill="#333">58</text><line x1="112.3" y1="43" x2="112.3" y2="57" stroke="#333" stroke-width="1.5"/><text x="112.3" y="72" text-anchor="middle" font-size="13" fill="#333">59</text><line x1="157.4" y1="43" x2="157.4" y2="57" stroke="#333" stroke-width="1.5"/><text x="157.4" y="72" text-anchor="middle" font-size="13" fill="#333">60</text><line x1="202.6" y1="43" x2="202.6" y2="57" stroke="#333" stroke-width="1.5"/><text x="202.6" y="72" text-anchor="middle" font-size="13" fill="#333">61</text><line x1="247.7" y1="43" x2="247.7" y2="57" stroke="#333" stroke-width="1.5"/><text x="247.7" y="72" text-anchor="middle" font-size="13" fill="#333">62</text><line x1="292.9" y1="43" x2="292.9" y2="57" stroke="#333" stroke-width="1.5"/><text x="292.9" y="72" text-anchor="middle" font-size="13" fill="#333">63</text><line x1="338" y1="43" x2="338" y2="57" stroke="#333" stroke-width="1.5"/><text x="338" y="72" text-anchor="middle" font-size="13" fill="#333">64</text><circle cx="292.9" cy="50" r="5" fill="#ffffff" stroke="#333" stroke-width="1.5"/><circle cx="67.1" cy="50" r="5" fill="#e06666" stroke="#333" stroke-width="1"/><text x="67.1" y="30" text-anchor="middle" font-size="13" fill="#333">start</text><text x="292.9" y="30" text-anchor="middle" font-size="13" fill="#333">stop</text></svg>
Your Turn:
- Prompt: Start at $58$ and count on to $63$.
- Answer: $58, 59, 60, 61, 62, 63$.
Example 2: Past one hundred, from 87
Problem: Start at $87$ and count aloud to $120$. What are the three numbers after $99$?
Solution:
- Count up to the next decade: $87, 88, 89, 90$.
- Keep counting by ones: $91, 92, \ldots, 99$.
- After $99$ comes $100$. Why: ten tens make one hundred, and the road keeps going.
- Now the small numbers start again after the hundred: $101, 102, 103$, and so on to $110$, then $111, \ldots, 120$.
Answer: The three numbers after $99$ are $100, 101, 102$. The count ends $\ldots, 118, 119, 120$.
> Verification & Check: Each number after $100$ is $100$ plus a small number: one hundred one is $100$ and $1$ more, one hundred two is $100$ and $2$ more.
Your Turn:
- Prompt: Start at $95$ and count on to $105$.
- Answer: $95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105$.
Example 3: Count a big pile by tens and ones
Problem: Noah has $6$ bags with ten crayons in each bag, and $4$ loose crayons. How many crayons?
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 220 170" width="220" height="170" role="img" aria-label="Six ten-rods and four single cubes: 6 bags of ten crayons and 4 loose crayons."
The chapter continues in the book.