30-minute lesson
Year 2 Mathematics: Numbers to 120: tens and ones
Lesson objective
- Count forwards and backwards by ones from any number up to 120.
- Count by tens from 0 to 120.
- Show a two-digit number as tens and ones using bundles and loose objects.
Success criteria:
- I can count on from any number to 120.
- I can count by tens to 120.
- I can show a number like 34 as 3 tens and 4 ones.
- I can say which of two numbers is bigger.
Materials
- About 120 pop sticks, straws or dry pasta tubes
- Rubber bands or hair ties for making bundles of ten
- Two plastic cups labelled 'tens' and 'ones'
- Paper and a pencil
Introduction
3 minIntroduce today's words:
- ones: Single objects that are not grouped.
- tens: Groups of ten objects bundled together.
- digit: One of the symbols 0 to 9 used to write numbers.
- bundle: A group of ten objects held together, such as 10 pop sticks with a rubber band.
- greater than: Bigger than; further along the counting sequence.
Ask your child what they already know about numbers to 120: tens and ones.
Explanation
6 minCounting a big pile one at a time is slow and easy to lose track of. Grouping objects into tens makes large numbers much easier to count and to understand.
Give your child a pile of pop sticks. Ask them to count out 10 and put a rubber band around them to make a bundle. Keep making bundles until there are not enough sticks left to make another one.
Now count the bundles by tens — 10, 20, 30 — and then count on the loose sticks by ones. For 3 bundles and 4 loose sticks, say '10, 20, 30, 31, 32, 33, 34.'
Show how the number is written. In 34, the 3 tells us there are 3 tens and the 4 tells us there are 4 ones. The position of a digit changes its value: 34 and 43 use the same digits but are different numbers.
When there are 10 bundles of ten, we have 100. Keep counting past 100: 101, 102 … up to 120. Many children say 'one hundred and ten' as 110; let them build it with 11 bundles to see why.
To compare two numbers, look at the tens first. 71 has 7 tens and 17 has only 1 ten, so 71 is greater.
- Count tens first, then ones.
- In a two-digit number, the left digit shows tens and the right digit shows ones.
Worked examples
5 minCounting a big pile of pasta
A pile of pasta tubes is grouped into 5 bundles of ten with 7 loose tubes left over. How many tubes are there?
Step 1: Count the bundles by tens: 10, 20, 30, 40, 50.
Step 2: Count on the loose tubes by ones: 51, 52, 53, 54, 55, 56, 57.
Step 3: 5 tens and 7 ones is written as 57.
Answer: There are 57 pasta tubes.
Which number is bigger?
Which is bigger, 48 or 84?
Step 1: 48 has 4 tens and 8 ones.
Step 2: 84 has 8 tens and 4 ones.
Step 3: Compare the tens first: 8 tens is more than 4 tens.
Answer: 84 is bigger than 48.
Counting past 100
Count on 3 from 108.
Step 1: Start at 108 and keep it in your head.
Step 2: Count on three: 109, 110, 111.
Answer: 3 more than 108 is 111.
Guided practice (do together)
6 min1. There are 3 bundles of ten pop sticks and 4 loose sticks. How many sticks altogether?
(a) 7 (b) 34 (c) 43 (d) 304
2. What number comes straight after 99?
3. In the number 58, what does the 5 stand for?
(a) 5 tens (b) 5 ones (c) 5 hundreds (d) 50 tens
4. What number is 6 tens and 2 ones?
Independent practice
7 min5. Which number is bigger: 17 or 71?
(a) 17 (b) 71 (c) They are the same
6. Count by tens and fill the gap: 40, 50, 60, ___
7. Which number comes between 109 and 111?
(a) 119 (b) 101 (c) 120 (d) 110
8. How many tens are there in 90?
Questions to check understanding
- Can you count on from any number to 120?
- Can you count by tens to 120?
- Can you show a number like 34 as 3 tens and 4 ones?
- Can you say which of two numbers is bigger?
- What was the trickiest part today?
Answer guide
1. 34 — 3 tens is 30, and 4 ones more makes 34.
2. 100 — After 99 we have 10 tens, which is 100.
3. 5 tens — The 5 is in the tens place, so it means 5 tens, which is 50.
4. 62 — 6 tens is 60, plus 2 ones makes 62.
5. 71 — 71 has 7 tens and 17 has only 1 ten, so 71 is bigger.
6. 70 — Counting by tens, after 60 comes 70.
7. 110 — Counting 109, 110, 111 — the number in between is 110.
8. 9 — Counting by tens to 90: 10, 20, 30, 40, 50, 60, 70, 80, 90 is 9 tens.
Review
3 minRecap the success criteria together. Watch for these common misconceptions:
- Writing 'one hundred and five' as 1005. Build it with 10 bundles and 5 loose sticks to show it is 105.
- Thinking 34 and 43 are the same because they use the same digits. Build both with bundles to compare.
- Losing track when counting over a 'decade' (for example 29, 30). Practise counting across tens slowly with a hundreds chart or a tape measure.
Extension activities
- Make a hundreds chart on paper and play 'guess my number' using clues such as 'it has 4 tens and is odd'.
- Count a jar of coins or buttons by grouping into tens first, then estimate the total before counting the next jar.
- Count by tens starting from a number other than 0, such as 3, 13, 23, 33.
Suggested follow-up
- Revisit numbers to 120: tens and ones tomorrow with two or three quick questions from memory.
- Try the online practice check for this topic and look at any questions that need another go.
Tips for parents
- Keep the bundles of ten — they are useful all year for adding, subtracting and comparing.
- A tape measure is a handy number line for counting to 120 and beyond.
- Ask your child to show numbers in more than one way: with bundles, by writing it, and by saying it.