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Decimals. The Five Important Principles. Principle One. Decimals extend the place value system to represent parts of the whole. Write four ones and two tenths as a decimal. 4.2 Write six ones, four tenths and two hundredths as a decimal. 6.42
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Decimals The Five Important Principles
Principle One • Decimals extend the place value system to represent parts of the whole. • Write four ones and two tenths as a decimal. • 4.2 • Write six ones, four tenths and two hundredths as a decimal. • 6.42 • Why do we need a decimal before the 10ths place? • Otherwise 2.0 would look like 20.
Principle Two • The base ten place value system is built on symmetry around the ones place. • Draw an example of a line of symmetry on your white board. • 100 10 1. 10ths 100ths line of symmetry
Principle Three • Decimals represent parts of a whole, whole numbers and mixed numbers. • Write 0.32 as a fraction. • 32/100 • Write 3.2 as a mixed number • 3 2/10 • Write 3.2 as an improper fraction. • 32/10 • Write 3.0 as an improper fraction and whole number • 30/10 or 3
Principle Four • Decimals can be interpreted and read in more than one way. • On your white board, find different ways to show the decimal 3.2
Principle Five • Decimals can be renamed as other decimals or fractions. • Using your white board or chart paper, shade 20 squares out of a hundred square grid. • Describe as: • Three fractions • 20/100 = 2/10=1/5 • Two decimals • 0.20 and 0.2
0.2 and 0.20 • Are these decimals equivalent? • Yes, because 20/100 and 2/10 are equivalent • Yes, because 0.2 equals 2 tenths and 0.20 equals 2 tenths and zero hundredths. • In measurement we must be more precise though and use more decimal places. There is a lot of difference between 3.20 metres and 3.2 metres when you are building a bridge! The more decimal places, the more precise the measurement.
Equivalent Fractions and Decimals • Find the decimal equivalent: • ½ • 0.5 or 0.50 • ¼ • 0.25 • 1/8 • 0.125 • How did we do this? • Find the decimal equivalent of 1/3 by dividing the denominator into the numerator. • This is a repeating decimal. • Why does it repeat? • We show this by placing a line over it.