How many objects do you see? Count and specify the number. 

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If we have less than 10 items, it is easy to count them one by one. But if there are more than 10 items, it takes a very long time to calculate them in this way. We may find the number of several items in groups of two, three, four objects. It means that you do not need to count each item, but groups of items that contain an equal number of objects: two, three, four, five. How do we calculate items by three? Use a number line from 1 to 20, with every third number highlighted:

1_2_3_4_5_6_7_8_9_10_11_12_13_14_15_16_17_18_19_20.

Call each three items the third number of the row in the following order: 3_6_9_12_15_18. For example, you need to count nuts. When taking three nuts, call the number 3. Then take three more nuts and name the number 6. For the following three nuts, we will use the number 9. Count until the nuts come to an end. Did it happen when you said 15? So, you have 15 nuts. If it turns out that there are two uncounted nuts left, continue counting from 15, adding one at a time: 16, 17. The total number of nuts is 17.

 

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