B. Number · Number Sense: Numbers to 50 and FractionsCounting to 50 by 1s, 2s, 5s and 10s
B1.5About 30 minutes
Learning goals- I can count to 50 by 1s.
- I can count to 50 by 2s, 5s and 10s.
- I can count objects by putting them in groups.
- I can count backward from a number.
Words to know
count
Say numbers in order to find out how many there are.
skip count
Count by jumping over numbers, like 2, 4, 6, 8 (counting by 2s).
group
A set of things that belong together, like a pair of mittens (2) or the fingers on one hand (5).
pair
Two things that go together, like two socks or two boots.
pattern
Something that repeats or changes in the same way each time.
Let's get counting!
The coach of a hockey team has a big bucket of pucks. Before practice, she needs to know how many pucks there are. How can she find out?
She can count them! Counting is one of the most important things we do in math. Today you will learn four ways to count: by 1s, by 2s, by 5s and by 10s.
Counting by 1s
When we count by 1s, we say every number in order: 1, 2, 3, 4, 5, and so on.
Here are the rules for good counting:
- Say the numbers in the right order.
- Give each object one number. Do not skip any object and do not count any object twice.
- The last number you say tells you how many there are altogether.
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Count the maple leaves by 1s. Touch each leaf as you say a number. There are 23 maple leaves.Counting trick
Touch each thing as you count it, or move it to a new pile. That way you will not count anything twice or miss anything!
The number chart
Here are the numbers from 1 to 50. Read each row from left to right. When you get to the end of a row, go down to the start of the next row.
Look at the rows. Each new row starts after a ten: 10, 20, 30, 40. Look down a column: the last digit stays the same! (1, 11, 21, 31, 41 all end in 1.)
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 |
| 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 |
| 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 |
Watch out!
The tricky spots are the numbers that come after a number ending in 9. After 29 comes 30. After 39 comes 40. After 49 comes 50.
Counting by 2s
Some things come in pairs: mittens, boots, socks, eyes, ears. When things come in twos, we can skip count by 2s. We jump over every other number:
2, 4, 6, 8, 10, 12, 14, 16, 18, 20 ...
Counting by 2s is faster than counting by 1s because each number counts two things at once.
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6 pairs of mittens. Count by 2s, one pair at a time: 2, 4, 6, 8, 10, 12. There are 12 mittens.Counting by 2s is like hopping 2 spaces at a time on the number line.When you count by 2s starting at 0 or 2, every number you say ends in 0, 2, 4, 6 or 8. These are called even numbers. Here are the 2s all the way to 50:
2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50
Counting by 5s
Hold up one hand. How many fingers? 5! When things come in groups of 5, we can skip count by 5s:
5, 10, 15, 20, 25, 30, 35, 40, 45, 50
Notice the pattern: the numbers end in 5, 0, 5, 0, 5, 0 ...
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6 hands. Each hand has 5 fingers. Count by 5s: 5, 10, 15, 20, 25, 30. That is 30 fingers.Ten jumps of 5 take you from 0 all the way to 50.Counting by 10s
A ten frame holds exactly 10. When we have full groups of 10, we can count by 10s. This is the fastest way!
10, 20, 30, 40, 50
Counting by 10s is just like counting 1, 2, 3, 4, 5, but we say ten, twenty, thirty, forty, fifty.
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Worked exampleCounting crayons
Leo has 3 full boxes of crayons with 10 crayons in each box. He also has 5 loose crayons. How many crayons does he have?
- Count the boxes by 10s: 10, 20, 30.
- Now keep going by 1s for the loose crayons: 31, 32, 33, 34, 35.
- The last number we said was 35.
Worked exampleCounting boots at the door
After recess on a snowy day, there are 9 pairs of boots by the classroom door. How many boots are there?
- Each pair has 2 boots, so count by 2s.
- Put up one finger for each pair as you count: 2, 4, 6, 8, 10, 12, 14, 16, 18.
- We counted 9 pairs (9 fingers) and stopped at 18.
Worked exampleCounting backward
A rocket is about to blast off! Count backward from 10 by 1s. Then count backward from 50 by 10s.
- Counting backward means each number is one less than the one before.
- From 10 by 1s: 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 ... Blast off!
- From 50 by 10s: 50, 40, 30, 20, 10, 0.
Backward by 1s: 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0. Backward by 10s: 50, 40, 30, 20, 10, 0.
Choose a smart way
Which way should I count? Look at how the things are grouped:
- Loose things? Count by 1s.
- Things in pairs? Count by 2s.
- Things in groups of five (like fingers or tally marks)? Count by 5s.
- Things in full groups of ten (like ten frames or crayon boxes)? Count by 10s.
Just for funWhat if you counted by 1s every second, all day and all night, without stopping? It would take you more than 11 days to count to one million!
Hands-on activityCereal counting challenge
You need: a small bowl of dry cereal (O-shaped cereal works well), dried beans or buttons, and a few small cups or an empty egg carton.
- Grab a big handful. Guess how many you have.
- Count them by 1s, moving each one as you count.
- Now put them in pairs and count by 2s. Did you get the same number?
- Put them in groups of 5 and count by 5s.
- Put them in groups of 10 (one group in each cup) and count by 10s, then count the leftovers by 1s.
- Talk about it: Which way was fastest? Why do you always get the same total?
Hands-on activityHop and count
Make a hopscotch path with tape or sidewalk chalk. Hop and say the numbers by 2s. Then do jumping jacks and count by 5s: say a number on every jump (5, 10, 15 ...). Try to reach 50!
Your turn!
1Count by 2s. What comes next? 2, 4, 6, \_\_, \_\_
2Count by 5s. Fill in the missing number: 5, 10, 15, \_\_, 25
3Count by 10s from 10 to 50.
4What number comes right after 29?
5Fill in the missing number: 36, 37, \_\_, 39
6There are 4 hands. How many fingers? Count by 5s.
5, 10, 15, 20. There are 20 fingers.
7There are 7 pairs of skates. How many skates are there?
2, 4, 6, 8, 10, 12, 14. There are 14 skates.
8Count backward by 1s: 25, 24, 23, \_\_, \_\_
Keep trying
Did a number get mixed up? That's okay! Good mathematicians check their work and try again. Counting twice is a smart way to check.
More practice: warm-up
1Count by 10s. Fill in the missing numbers: 10, 20, \_\_, 40, \_\_
2How many ducks are on the pond? Count by 1s.
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There are 9 ducks. (1, 2, 3, 4, 5, 6, 7, 8, 9)
3What number comes right after 49?
4Count by 2s. What comes next? 10, 12, 14, \_\_, \_\_
5True or false: When we count by 5s (5, 10, 15 ...), every number ends in 5 or 0.
True. The numbers go 5, 10, 15, 20 ... so they end in 5, 0, 5, 0 ...
More practice: on your own
1Count the socks by 2s. There is a space after each pair.
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There are 8 pairs. Count by 2s, one pair at a time: 2, 4, 6, 8, 10, 12, 14, 16. There are 16 socks.
2Count by 5s. Fill in the missing numbers: 30, 35, \_\_, 45, \_\_
40 and 50. Each number is 5 more than the one before.
3Count backward by 10s: 40, 30, \_\_, \_\_, \_\_
20, 10, 0. Each number is one ten less.
4Amir has 2 bundles of popsicle sticks with 10 sticks in each bundle. He also has 7 loose sticks. How many sticks does he have?
Count the bundles by 10s: 10, 20. Then count the loose sticks by 1s: 21, 22, 23, 24, 25, 26, 27. He has 27 sticks.
5Each sticker sheet has 5 star stickers. Nia has 7 sheets. Which is the smartest way to count: by 1s, 2s, 5s or 10s? How many stars?
By 5s, because the stars are in groups of 5. 5, 10, 15, 20, 25, 30, 35. There are 35 stars.
Challenge
1Find the mistake! Ravi counted by 2s like this: 2, 4, 6, 8, 10, 11, 12. What did he do wrong? What should he say after 10?
After 10, Ravi switched to counting by 1s (11, 12). Counting by 2s jumps over a number each time. After 10 he should say 12, 14.
2Zara counted 23 hockey pucks. Then she counted them again, starting with a different puck. Will she get 23 again? How do you know?
Yes, 23 again. The pucks did not change. As long as she gives each puck one number and does not skip or double-count, the last number will be the same, no matter where she starts.
3The coach has 2 bags with 10 pucks in each bag, and 4 small piles with 5 pucks in each pile. How many pucks are there altogether? Explain how you counted.
Count the bags by 10s: 10, 20. Then keep going by 5s for the piles: 25, 30, 35, 40. There are 40 pucks.
Quiz
1. Count by 5s: 5, 10, 15, 20, ___. What comes next?
2. Which list shows counting by 10s?
3. There are 5 pairs of mittens. How many mittens are there?
4. What number comes after 39?
5. Ella counted 4 full ten frames and 2 more dots. How many dots?
6. Count backward by 1s: 43, 42, 41, ___. What comes next?
7. What is the fastest way to count 5 full ten frames?
What your child is learning: to count to 50 by 1s, and to skip count by 2s, 5s and 10s. Skip counting is the foundation for later work with place value, adding and multiplying.
Common mistakes and how to help:
- Skipping or double-counting objects. Encourage your child to touch or move each object as they count it.
- Getting stuck at the "decade" numbers. Children often say "twenty-nine, twenty-ten". Practise the change from 9 to the next ten: 19 to 20, 29 to 30, 39 to 40, 49 to 50. The number chart helps: the next number is at the start of the next row.
- Not knowing the last number is the total. After counting, ask "So how many are there?" If your child counts again, model that the last number said is the answer.
- Losing track when skip counting objects. Have your child group the objects first (pairs, fives or tens), then count the groups.
Everyday practice: count stairs, count by 2s when putting socks away, count by 5s using nickels or fingers, count by 10s with bundles of 10 straws or popsicle sticks. Count backward while waiting at a red light.
Math talk questions: "How did you know what comes next?" "Which way of counting was faster? Why?" "What pattern do you see in the numbers?"