- 1). Write the four lengths on a piece of paper, with each length beneath the other. Given the side lengths of 4.25, 8.353, 4.25 and 8.353, you would write the following:
4.25
8.353
4.25
8.353 +
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Make sure the decimal point are aligned. - 2). Fill in missing zeros. Notice how 4.25 and 8.353 have a different number of digits to the right of the decimal point. Because 4.25 has only 2 digits to the right of the decimal point and 8.353 has 3 digits to the right of the decimal point, you must insert a 0 after 4.25:
4.250
8.353
4.250
8.353 +
--------------- - 3). Add the four lengths like you would add regular whole numbers. Given the example, add as if you are adding 4250, 8353, 4250 and 8353:
4250
8353
4250
8353 +
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25206 - 4). Add the missing decimal point. Given the example, there were three digits after the decimal point. So you would add the decimal so that, once again, there are three digits after the decimal. Thus, 25206 would turn into 25.206 -- which is the perimeter of the rectangle.
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