Đếm hình phẳng trong hình ghép, đếm que

1. Count one size at a time

A grid of squares hides squares of several sizes. The smallest size is a single cell. A bigger one is made of four cells together. Count every small square first. Then move on to the bigger size. Finally add all the sizes together.

2. A 2 by 2 grid

This grid has 4 small cells. The four cells also form 1 big square. So there are 4 plus 1, that is 5 squares. Many children forget the big square.

3. A 2 by 3 grid

This grid has 6 small cells. There are 2 squares of the double size. One sits on the left and one on the right. Altogether 6 plus 2 gives 8 squares.

4. Counting triangles

Number each small triangle on the figure. Count all the small ones and write the number down. Then look for big triangles made of small ones. Write down each big triangle only once.

5. Counting matchsticks

Two squares side by side share one stick. So you must not count that stick twice. One square needs 4 sticks. Each extra square needs only 3 more sticks. Three squares in a row need 10 sticks.

6. Check your answer

Count a second time in the same order. If both counts agree, your answer is safe.