B. Number · Number Sense: Numbers to 200 and Fractions

Counting to 200 by 1s, 10s, 20s, 25s and 50s

B1.4About 35 minutes

Learning goals

I can count forward and backward by 1s to 200, even past 100.
I can count by 10s from any number.
I can count by 20s, 25s and 50s to 200.
I can choose a skip-counting number that makes counting faster.

Words to know

skip count
Counting by jumping the same amount each time, like 20, 40, 60.

hundred
Ten groups of ten. We write it as 100.

pattern
Something that repeats or grows in the same way each time.

count backward
Counting down, getting smaller each time, like 105, 104, 103.

Remember from Grade 1

In Grade 1 you learned to count to 50. You counted by 1s, 2s, 5s and 10s.

This year you will count all the way to 200! That's four times as far as 50.

Imagine the whole class collects pop can tabs for a school project. Soon there are more than 100 tabs. How do we keep counting? Let's find out.

Counting past 100

After 99 comes 100 (one hundred). Then the counting starts over, but with "one hundred" in front:

101, 102, 103 ... 109, 110, 111 ...

We say: "one hundred one, one hundred two, one hundred three ..."

The ones and tens repeat the same pattern you already know. Only the hundreds part is new.


101	102	103	104	105	106	107	108	109	110
111	112	113	114	115	116	117	118	119	120
121	122	123	124	125	126	127	128	129	130
...
191	192	193	194	195	196	197	198	199	200

Part of a hundreds chart from 101 to 200. Look down a column: the ones digit stays the same and the tens go up by 1.

Tricky spots

Watch out when the tens change!

108, 109, 110 (not 1010)
118, 119, 120
198, 199, 200

When you get to a 9 in the ones place, the next number starts a new ten.

Counting by 10s from any number

When you count by 10s, the ones digit stays the same. Only the tens go up.

34, 44, 54, 64, 74, 84, 94, 104, 114 ...

Look! After 94 comes 104. That's "one hundred four". We passed 100 and kept going.

Counting by 20s from 100: 120, 140, 160, 180, 200. Each jump of 20 is two jumps of 10.

Counting by 20s, 25s and 50s

Big skip counts help us count big groups fast.

By 20s: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200. (It is like counting by 2s, then adding a zero.)
By 25s: 25, 50, 75, 100, 125, 150, 175, 200.
By 50s: 50, 100, 150, 200.

Counting by 25s: 8 jumps of 25 take you from 0 to 200.

Quarters count by 25s

A Canadian quarter is worth 25 cents. To count quarters, count by 25s: 25, 50, 75, 100. Four quarters make 100 cents, which is one dollar!

Notice the pattern for 25s: the numbers end in 25, 50, 75, 00, over and over.

Counting backward

We can also count down. Going backward, the numbers get smaller.

By 1s: 104, 103, 102, 101, 100, 99, 98
By 10s: 200, 190, 180, 170, 160
By 50s: 200, 150, 100, 50, 0

Worked example

Example 1: Boxes of crayons

The art room has 7 boxes of crayons. Each box holds 20 crayons. How many crayons are there?

Each box has 20, so count by 20s, one number for each box.
Touch each box as you count: 20, 40, 60, 80, 100, 120, 140.
We said 7 numbers for 7 boxes. The last number is 140.

There are 140 crayons.

Worked example

Example 2: Counting on by 10s

Sam has 56 hockey cards. His uncle gives him 5 packs of 10 cards. How many cards does he have now?

Start at 56. Don't count the first 56 one by one!
Count on by 10s for each pack. The ones digit stays a 6: 66, 76, 86, 96, 106.
Five packs, five jumps of 10.

Sam has 106 hockey cards.

Worked example

Example 3: Counting backward by 1s past 100

Count backward from 103 to 97.

103, 102, 101 ... what comes before 101? 100.
What comes before 100? 99. The hundreds are gone now.
Keep going: 98, 97.

103, 102, 101, 100, 99, 98, 97

Just for fun

Why was 6 afraid of 7?

Because 7 8 9! (Say it out loud: seven ate nine.)

Hands-on activity

Count a big collection

You need: lots of small things (dry pasta, beans, Lego bricks or cereal O's) and some small cups or paper plates.

Count out 10 things into each cup. Make as many cups as you can (try for 10 to 20 cups).
Count the cups by 10s: 10, 20, 30 ...
Now put two cups together and count by 20s. Did you get the same total?
Grown-up: make piles of 25 and count by 25s together.
Count backward by 10s as you put the cups away.

Math talk: "Which way of counting was fastest? Why?"

Your turn

Count by 1s: 116, 117, 118, __, __, __

Count by 10s: 72, 82, 92, __, __, __

Count by 20s from 100 to 200.

Count by 25s: 25, 50, __, __, __, 150

Count backward by 10s: 180, 170, __, __, __

Count by 50s to 200.

How many cents are 3 quarters? Count by 25s.

More practice: warm-up

What number comes after 109?

What number comes before 200?

Count by 10s: 110, 120, __, __

Count by 1s backward: 101, 100, __

Count by 50s: 0, 50, __

More practice: on your own

Fill in the missing numbers: 147, 148, 149, __, __

Count by 10s from 63 until you pass 120.

Count backward by 1s from 152 to 146.

6 bags each have 25 marbles. How many marbles in all?

Which skip count would you use to count 9 cartons with 20 eggs each? What is the total?

Challenge

Mia counts by 20s and Leo counts by 25s. They both start at 0. Which numbers do they both say before 200? (Include 200.)

Find the mistake: "190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 1100".

Ava wants to count from 0 to 200. Counting by 50s takes 4 jumps. How many jumps does counting by 25s take? Why?

Check your understanding

Quiz

What comes next? 117, 118, 119, __

Count by 10s: 85, 95, 105, __

Which list counts by 25s?

How many 50s make 200?

Count backward: 102, 101, 100, __

There are 8 boxes of 20 pencils. How many pencils?

For parents and teachers

Big idea: Counting past 100 follows the same pattern as counting to 100, with "one hundred" in front. Skip counting by 20s, 25s and 50s is a fast way to count big collections.

Common difficulties:

Bridging tens and hundreds (saying "one hundred nine, one hundred ten" is easy, but some children say "1010" or skip from 199 to 1100). Practise the "9 to 0" spots out loud.
Counting by 10s from a number that doesn't end in 0 (34, 44, 54). Use a hundreds chart and point straight down a column.
Counting backward past 100 (101, 100, 99). Many children get stuck here. Practise with a number line.
Losing track when skip counting objects. Have your child touch or move each group as they say each number.

How to help: Count real collections together: coins, pasta, pages in a book. Count quarters by 25s. In the car, take turns counting by 20s or backward by 10s from 200. Let your child choose which skip count to use and ask why.