Call each pair a number in order: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20…, until you count all the pairs. 

There are 18 clouds in total.

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Here is a compass. 

With its help, people determine the right direction if they suddenly get lost and can not find their way home. Now there is a navigator, and a compass is almost unnecessary. But let’s discuss something interesting about it. Look at divisions and numbers. There are more divisions than numbers. And the numbers are arranged in a circle, starting with 0. The next number is 20, then - 40. It was done to fit as many numbers as possible up to 360. After all, there is not enough space on such a small device. And all these numbers are important for those who know how to use a compass. We call this way of arranging numbers skip-counting, as we do not count every number, but each 2, 10, and even 20. 

If the objects are arranged by pairs, we can easily count them by 2s. It means we will call each pair a number. As we count 2 objects at a time, we need to say numbers, skipping over one. We call each pair every second number of the number line.

Let’s mark every second number in the number line:  

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

We will use the numbers marked red, giving a name to each pair.

Let’s write them out: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20. Now, let’s count the objects in the picture below.

Triangles are not paired. But we will pair them up when counting. 

Or, when counting, we may not circle but cross out the figures in pairs.

Choose any convenient way for you.

The last group of 2 triangles we called number 16. It denotes the number of all triangles.  

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