Specify each object as a number in order from 1 to 20. If you mark the last item with the number 17, there are 17 images in total.

Do not miss a single object, and do not count the same item twice.

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People began to indicate the number of objects using signs much later than they learned to count. When it became necessary to remember the result of the calculation, they started to write it down. Some used hieroglyphic icons, others sticks, and dots, or letters. But the meaning was similar.

People showed the numbers by repeating some symbol with their fingers: I - one, / / - two, ᐁ ᐁ ᐁ - three, X X X X - four. The number was in a separate group. They drew a palm, and everyone knew it meant five because it indicates the number of fingers on the hand. Two palms denoted the number ten.

Later, the number 10 was allocated to a separate unit of account because it is convenient to count tens. You can use tens when counting a large number of items. Now we also distinguish ones and tens in numbers. It allows us to perform operations with numbers that are greater than ten.

Over the years, people have come to a single system of writing down numbers. But the principles of counting have not changed. We still call each item in the order, starting from 1. We do not skip items when counting and do not count one item twice. We determine their total number according to the number we called the last item. To calculate correctly, you need to learn a sequence of numbers: 1_2_3_4_5_6_7_8_9_10_11_12_13_14_15_16_17_18_19_20.

Count all the items in each task.

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