Practice subtraction

### 1.1. Solve the exercises in the textbook Practice page 54

**Lesson 1 Textbook page 54**

Calculate then calculate

a) 68.72−29.91 b) 52.37−8.64

c) 75.5−30.26 d) 60−12.45.

__Solution guide:__

a) \(\begin{array}{*{20}{c}}

{ – \underline \begin{array}{l}

68.72\\

29.91

\end{array} }\\

{38,81}

\end{array}\)

b) \(\begin{array}{*{20}{c}}

{ – \underline \begin{array}{l}

52.37\\

\,\,8,64

\end{array} }\\

{43,73}

\end{array}\)

c) \(\begin{array}{*{20}{c}}

{ – \underline \begin{array}{l}

75.50\\

30.26

\end{array} }\\

{\,\,\,\,45,24}

\end{array}\)

d) \(\begin{array}{*{20}{c}}

{ – \underline \begin{array}{l}

60.00\\

12.45

\end{array} }\\

{\,\,\,\,47,55}

\end{array}\)

Lesson 2 Textbook page 54

a) x + 4.32 = 8.67 b) 6.85 + x = 10.29

c) x – 3.64 = 5.86 d)7.9 – x = 2.5

__Solution guide:__

a) x+4.32=8.67

x=8.67−4.32

x=4.35

b) 6.85+x=10.29

x=10.29−6.85

x=3.44

c) x−3.64=5.86

x=5.86+3.64

x=9.5

d) 7.9−x=2.5

x=7.9−2.5

x=5.4

Lesson 3 Textbook page 54

Three melons weigh 14.5kg. The first fruit weighs 4.8kg, the second one is 1.2kg lighter than the first one. How many kilograms does the third fruit weigh?

__Solution guide:__

The second fruit in kilograms is:

4.8−1.2=3.6(kg)

Both heads weigh in kilograms:

4.8+3.6=8.4(kg)

The third fruit in kilograms is:

14.5−8.4=6.1(kg)

Answer: 6.1kg

Lesson 4 Textbook page 54

a) Calculate and compare the values of a−b−c and a−(b+c)

a | b | c | a – b – c | a – (b + c) |

8.9 | 2.3 | 3.5 | ||

12.38 | 4.3 | 2.08 | ||

16.72 | 8.4 | 3.6 |

b) Calculated in two ways:

8.3−1,4−3,6 18.64−(6.24+10.5)

__Solution guide:__

a)

a | b | c | a – b – c | a – (b + c) |

8.9 | 2.3 | 3.5 | 8.9-2.3-3.5=3.1 | 8.9-(2,3+3.5)=3.1 |

12.38 | 4.3 | 2.08 | 12.38-4.3-2.08=6 | 12.38-(4.3+2.08)=6 |

16.72 | 8.4 | 3.6 | 16.72-8.4-3.6=4.72 | 16.72-(8.4+3.6)=4.72 |

Comment: a−b−c=a−(b+c)

b)

– Calculation: 8.3−1,4−3.6

Option 1: 8.3−1,4−3.6=6.9−3.6=3.3

Option 2: 8.3−1,4−3,68.3−1,4−3,6

=8.3−(1,4+3,6)

=8.3−5=3.3

– Calculation: 18.64−(6.24+10.5)

Method 1: 18.64−(6.24+10.5)

=18.64−16.74=1.9

Method 2: 18.64−(6.24+10.5)

=18.64−6.24−10.5

=12.4−10.5

= 1.9

.

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