Decimals
NZ Level 5
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Subtract numbers with decimals using the standard subtraction algorithm
Lesson

We can subtract numbers that include decimals in just the same way as we would subtract whole numbers. We just need to line up the numbers according to their place value.

Examples

question 1

Evaluate: $21.952-5.719$21.9525.719

Think: How do the place value columns line up?

Do$21.952-5.719=16.233$21.9525.719=16.233

We can also use this for questions that involve money, distances or any number that involves decimals. 

Examples

question 2

Evaluate: $\$18.52-\$1.28$$18.52$1.28

Think: Line up the place value columns

Do: $\$18.52-\$1.28=\$17.24$$18.52$1.28=$17.24

 

Expressing decimals as fractions

Remember the names from the columns on the place value table- tenths, hundredths, thousandths and so on. When we convert decimals to fractions, these names tell us what the denominator (the bottom number) of our fractions will be.

Examples

question 3

Think: A mixed number is an answer with a whole number and a fraction

Do:

$7.45-3.7$7.453.7 $=$= $3.75$3.75
  $=$= $3\frac{75}{100}$375100
  $=$= $3\frac{3}{4}$334

 

Now let's use this to solve some questions!

Examples

question 4

Evaluate: Evaluate $0.94-0.3$0.940.3, giving your answer as a simplified fraction

ThinkTo simplify a fraction, we need to find common factors between the numerator and the denominator

Do: 

$0.94-0.3$0.940.3  $=$= $0.64$0.64  
  $=$= $\frac{64}{100}$64100  ($4$4 is a common factor)
  $=$= $\frac{16}{25}$1625  

 

QUESTION 5

Evaluate $9.9-5.5$9.95.5

  1.   $9$9 $.$. $9$9
    $-$ $5$5 $.$. $5$5
      $\editable{}$ $.$. $\editable{}$

 
QUESTION 6

Find $3-0.8$30.8, leaving your answer in decimal form.

 
QUESTION 7

Evaluate $8.2-2.13-4.938$8.22.134.938

Outcomes

NA5-3

Understand operations on fractions, decimals, percentages, and integers

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