Subtract two decimals

### 1.1. Knowledge to remember

**a) **__Example 1__: The curve ABC is 4.29m long, in which the straight line AB is 1.84m long. How many meters long is the line segment BC?

We have to do the subtraction: 4.29 – 1.84 = ? square meter

We have: 4.29m = 429 cm

1.84m = 184 cm

So: 4.29 – 1.84 = 2.45 (m)

Usually we set the calculation and then do the following:

- Perform subtraction like subtracting natural numbers.
- Write commas in the column difference with the commas of the subtracted and subtracted numbers.

**b)** __Example 2__: 45.8 – 19.26 = ?

- Let 45,8 be 45.80 and then subtract the natural numbers.
- Write commas in column difference with commas of numbers subtracted.

To subtract a decimal from a decimal, do the following:

– Write the minus number under the subtracted number so that the digits in the same row line up.

– Perform subtraction like subtracting natural numbers.

– Write commas in the column difference with commas of subtracted and subtracted numbers.

**Attention:** If the number of digits in the decimal part of the number to be subtracted is less than the number of digits in the decimal part of the subtracted number, we can write an appropriate number of zeros to the right of the decimal part of the subtracted number, and then subtract as a natural number.

### 1.2. Solve textbook exercises on page 54

**Lesson 1 of the textbook page 54:**

Calculate

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

{68.4}\\

{\,\,25,7}

\end{array}} ;b) – \underline {\begin{array}{*{20}{c}}

{46,8}\\

{\,\,9,34}

\end{array}} ;c) – \underline {\begin{array}{*{20}{c}}

{50,81}\\

{\,\,19,256}

\end{array}} \)

*Solution guide:*

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

{ – \underline {\begin{array}{*{20}{c}}

{68.4}\\

{\,\,25,7}

\end{array}} }\\

{\,\,\,\,\,42,7}

\end{array}\)

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

{\underline {\begin{array}{*{20}{c}}

{46,8}\\

{\,\,9,34}

\end{array}} }\\

{37,47}

\end{array}\)

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

{\underline {\begin{array}{*{20}{c}}

{50,81}\\

{\,\,19,256}

\end{array}} }\\

{31,554}

\end{array}\)

Lesson 2 Textbook page 54:

Calculate then calculate:

a) 72.1−30.4 b) 5.12−0.68 c) 69−7.85

*Solution guide:*

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

{\underline { – \begin{array}{*{20}{c}}

{72.1}\\

{\,\,30,4}

\end{array}} }\\

{\,\,\,\,\,41.7}

\end{array}\)

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

{\underline { – \begin{array}{*{20}{c}}

{5,12}\\

{\,\,0.68}

\end{array}} }\\

{\,\,\,\,\,4,44}

\end{array}\)

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

{\underline { – \begin{array}{*{20}{c}}

{69.00}\\

{\,\,7,85}

\end{array}} }\\

{\,\,\,\,\,61,15}

\end{array}\)

Lesson 3 Textbook page 54:

One box contains 28.75kg of sugar. People take out 10.5kg10.5kg of sugar from that barrel, then take out another 8kg of sugar. How many kilograms of sugar are left in the barrel?

*Solution guide:*

The total number of kilograms of sugar taken out is:

10.5+8=18.5(kg)

In the remaining barrel the number of kilograms of sugar is:

28.75−18.5=10.25(kg)

Answer: 10.25kg

.

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