When counting by pairs, call each pair a number in order - 2 4 6 8 10 12 14 16 18 20…

When counting by 5s, count each group of 5 items the following numbers - 5 10 15 20 25 30 35 40…

When counting by 10s, assign each set of 10 objects numbers in 10 - 10 20 30 40 50 60 70 80 90 100…

The number you called the last group when counting denotes the numbers of all objects.

Back to practice

How can we count shapes in the picture fast and conveniently? These objects are arranged in pairs, so we will count them by 2s. Let’s call each pair a number in order: 2, 4, 6, 8, 10, etc. What number did we call the last pair? It is the number of all figures.

How can we count these bananas?

First, let’s check how many bananas are in each bunch. All bunches contain 5 bananas, so we can count them skipping 5:

5 10 15 20 25 30 35

We have called the last 5 fruits the number 35. How many bananas are there? 35.

Here are a lot of tiny buttons, but they all are in sets of 10.

We can count by 10s: 10 20 30 40 50 60 70 80 90

There are 90 buttons in total.

There is one more way to count tens. First, we can count groups as usual: 1 2 3 4 5 6 7 8 9. These are 9 tens. Let’s denote the word “Ten” with the number 0 and write it on the right of 9. Thus, we get the number 90.

Back to practice