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Decimals: tenths and hundredths

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Apuntes de la lección

What is a decimal?

  • A decimal is a way to write numbers that are not whole, using a decimal point (.) to separate the whole part from the fraction part.
  • The decimal point is like a separator: numbers to the left are whole numbers, numbers to the right are parts of a whole.
  • In the number 3.7, the 3 is the whole part and the 7 is the fraction part.
  • Decimals are based on tenths and hundredths. The first digit after the point is tenths, the second is hundredths.
  • Example: In 0.5, the 5 is in the tenths place, so 0.5 means 5 tenths.

Tenths and hundredths as fractions

  • One tenth is written as 0.1 and as a fraction it is \frac{1}{10} .
  • One hundredth is written as 0.01 and as a fraction it is \frac{1}{100} .
  • The number 0.25 means 25 hundredths, which is the same as \frac{25}{100} .
  • You can write tenths as hundredths: 0.3 = 0.30, because 3 tenths = 30 hundredths.
  • Remember: 10 hundredths make 1 tenth, and 100 hundredths make 1 whole.

Place value after the decimal point

  • The first digit after the decimal point is in the tenths place.
  • The second digit after the decimal point is in the hundredths place.
  • In 0.47, the 4 is in the tenths place (4 tenths) and the 7 is in the hundredths place (7 hundredths).
  • The value of a digit depends on its place: in 0.62, the 6 is worth 6 tenths (0.6) and the 2 is worth 2 hundredths (0.02).
  • You can read 0.47 as 'four tenths and seven hundredths' or 'forty-seven hundredths'.

Comparing and ordering decimals

  • To compare decimals, look at the digits from left to right, starting with the whole number part.
  • If the whole parts are equal, compare the tenths digit. If those are equal, compare the hundredths digit.
  • Example: 0.5 is greater than 0.3 because 5 tenths is more than 3 tenths.
  • Example: 0.42 is less than 0.47 because they have the same tenths (4) but 2 hundredths is less than 7 hundredths.
  • You can also compare by thinking of fractions: 0.6 = 6/10 and 0.59 = 59/100, so 0.6 is greater because 60/100 > 59/100.

Decimals on a number line

  • You can place decimals on a number line between whole numbers.
  • The space between 0 and 1 can be divided into 10 equal parts for tenths.
  • Each tenth can be divided into 10 smaller parts for hundredths.
  • Example: 0.3 is three tenths of the way from 0 to 1.
  • Example: 0.25 is two tenths and five hundredths, which is a quarter of the way from 0 to 1.

Rounding decimals to the nearest whole number

  • Rounding means finding the closest whole number to a decimal.
  • Look at the digit in the tenths place. If it is 5 or more, round up. If it is 4 or less, round down.
  • Example: 3.7 rounds to 4 because the tenths digit is 7 (≥5).
  • Example: 3.4 rounds to 3 because the tenths digit is 4 (<5).
  • If the tenths digit is exactly 5, round up: 2.5 rounds to 3.

Decimals in money and measurement

  • Money uses decimals: £1.50 means 1 pound and 50 pence.
  • There are 100 pence in a pound, so 0.01 of a pound is 1 penny.
  • Measurements use decimals: 1.5 metres means 1 metre and 50 centimetres.
  • There are 100 centimetres in a metre, so 0.01 of a metre is 1 centimetre.
  • When solving problems with money or measurements, write the decimal correctly and use the units.

Equivalent decimals

  • Equivalent decimals are decimals that have the same value but look different.
  • Adding zeros at the end of a decimal does not change its value: 0.5 = 0.50 = 0.500.
  • Removing trailing zeros also does not change the value: 0.70 = 0.7.
  • This works because 0.5 is 5 tenths, and 0.50 is 50 hundredths, which is the same amount.
  • When comparing decimals, you can add zeros to make them have the same number of digits.

Writing fractions as decimals

  • Any fraction with denominator 10 or 100 can be written as a decimal.
  • For tenths: the numerator goes in the tenths place. Example: \frac{3}{10} = 0.3.
  • For hundredths: the numerator goes in the hundredths place. Example: \frac{25}{100} = 0.25.
  • If a fraction has denominator 10, you can write it as hundredths by multiplying top and bottom by 10: \frac{3}{10} = \frac{30}{100} = 0.30.
  • Practice: \frac{7}{10} = 0.7, \frac{9}{100} = 0.09.

Solving simple problems with decimals

  • Add and subtract decimals by lining up the decimal points.
  • Example: 0.4 + 0.3 = 0.7 because 4 tenths + 3 tenths = 7 tenths.
  • Example: 0.45 + 0.20 = 0.65 because 45 hundredths + 20 hundredths = 65 hundredths.
  • When adding or subtracting money, keep the pounds and pence separate: £2.50 + £1.25 = £3.75.
  • Check your answer by estimating with whole numbers.

Diapositivas

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Preguntas de práctica

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  1. 1.What is the decimal for the fraction 1/10?

    Easy
    • A0.1
    • B0.01
    • C1.0
    • D10.0
  2. 2.What is the decimal for the fraction 25/100?

    Easy
    • A0.25
    • B2.5
    • C0.025
    • D25.0
  3. 3.The decimal 0.3 is equal to the fraction 3/10.

    Easy

    True or false?

  4. 4.Order these decimals from smallest to largest: 0.3, 0.12, 0.25.

    Easy
    • 0.3
    • 0.12
    • 0.25
  5. 5.Which decimal is greater: 0.5 or 0.05?

    Medium
    • A0.5
    • B0.05
    • CThey are equal
    • DCannot tell
  6. 6.The decimal 0.20 is equal to 0.2.

    Medium

    True or false?

  7. 7.Which of the following is the correct way to write 35 hundredths as a decimal?

    Medium
    • A0.35
    • B3.5
    • C0.035
    • D35.0
  8. 8.Which of the following decimals are less than 0.5? (select all that apply)

    Medium
    • A0.45
    • B0.55
    • C0.09
    • D0.5
    • E0.3

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