Counting to 100: math lesson, Kindergarten

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Math lessons Kindergarten : Counting to 100 — Zyro the alien explorer of Planète Maths

How high can you count? In this chapter you will count from 0 all the way to 100. You will count by ones, then by tens, and you will learn how to start from any number and keep going. Get ready to say the numbers out loud, point at them, and write them!

Sommaire

1. Counting by ones

When you count by ones, every new number is exactly one more than the number before. Point at each object once, say one number for each object, and never skip or repeat an object.

Counting by onesCounting by ones means saying the numbers in order: 1, 2, 3, 4, 5, and so on. The last number you say tells you how many objects there are.

Look at the dots above. Ten dots are blue and three dots are orange. We say: ten, eleven, twelve, thirteen. So there are 13 dots.

Example 1: count the dotsCount the dots above. You say 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, then 11, 12, 13. The last number is 13, so there are 13 dots.

2. Counting by tens

Counting by ones to 100 takes a long time. A faster way is to count by tens. We make groups of ten and count one group at a time. Each new group adds ten more.

Counting by tensWhen you count by tens, you say: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. Ten tens make one hundred.

Each rod above has ten dots. One rod is 10. Two rods are 20. Three rods are 30. Four rods are 40. Five rods are 50.

Example 2: count the rodsThere are 5 rods with 10 dots in each rod. Count by tens: 10, 20, 30, 40, 50. There are 50 dots. In a number sentence: \(10 + 10 + 10 + 10 + 10 = 50\).

3. Counting on from any number

You do not always have to start at 1. You can start at any number and keep counting. This is called counting on. If you already know there are 7 blocks, you can say 8, 9, 10 to count three more blocks.

How to count on

Say the number you start with, but do not count it again.
Say the next number: it is one more.
Keep going, one number at a time, until you have counted all the new objects.

Example 3: count on from 7Start at 7 and count on 3 more: 8, 9, 10. You land on 10. On the number line you hop to the right three times.

4. Writing numbers 0 to 20

Numbers from 0 to 20 are the building blocks for bigger numbers. Here they are with their words. For the teen numbers, you can see one ten and some extra ones.

Number	Word	Tens and ones
0	zero	–
1	one	–
2	two	–
3	three	–
4	four	–
5	five	–
6	six	–
7	seven	–
8	eight	–
9	nine	–
10	ten	10
11	eleven	10 and 1
12	twelve	10 and 2
13	thirteen	10 and 3
14	fourteen	10 and 4
15	fifteen	10 and 5
16	sixteen	10 and 6
17	seventeen	10 and 7
18	eighteen	10 and 8
19	nineteen	10 and 9
20	twenty	20

To write a number, say it slowly and listen. “Fourteen” sounds like “four” and “teen”, so it is a ten and four more. We write it 14: a 1 for the ten and a 4 for the four ones.

Careful with the order of digitsThe number 13 has the 1 first and the 3 second. If you write 31 you have written a very different number: thirty-one. Say the number out loud and check each digit.

5. Number order and sequence

Numbers always come in the same order. A sequence is a list of numbers that follows a rule. When you count by ones, the rule is “add one”. When you count by tens, the rule is “add ten”. If you know the rule, you can find a missing number.

Before and afterThe number that comes right after a number is one more. The number that comes right before it is one less. For example, 26 comes right after 25 and right before 27.

Example 4: find the missing numbersLook at the strip: 24, 25, ?, 27, 28, ?. The first blank is between 25 and 27, so it is 26. The second blank comes after 28, so it is 29.

Zyro’s tipZyro the explorer says: “On my planet we count with our fingers too! When you hit nine, the next number is ten, and a brand new group of ten begins.”

6. Counting patterns on a hundred chart

A hundred chart is a big table with 10 rows and 10 columns. The first row goes from 1 to 10, the second row from 11 to 20, and so on until 100. Patterns help you count fast.

Look at the colored column. It shows all the numbers you say when you count by tens: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100. They all sit in the same column at the end of each row.

Move one step to the right: the number gets one more.
Move one step to the left: the number gets one less.
Move one row down: the number gets ten more.
Move one row up: the number gets ten less.

Example 5: use the chartPut your finger on 34. Move one row down and you land on 44, because 44 is ten more than 34. The numbers in a column all end with the same digit: 4, 14, 24, 34, 44.

7. Counting forward from a given number

Sometimes a teacher gives you a starting number and asks you to keep going. If you start at 58, you say 59, 60, 61, 62. Remember that after a number that ends in 9 you get a new ten: after 59 comes 60, and after 99 comes 100.

Watch the 9sAfter 29 comes 30, not “twenty-ten”. After 69 comes 70. The numbers ending in 9 are the tricky ones, so slow down there.