Topicmdc8210c2e0bf5757_1528449000663_0Topic

Subtraction of decimal fractions

Levelmdc8210c2e0bf5757_1528449084556_0Level

Second

Core curriculummdc8210c2e0bf5757_1528449076687_0Core curriculum

V. Operations on ordinary and decimal fractionsdecimal fractionsdecimal fractions. Student:
2) adds, subtracts, multiplies and divides decimal fractionsdecimal fractionsdecimal fractions in memory (in the simplest examples), or in writing and using a calculator (in difficult examples);
8) performs operations on decimal fractionsdecimal fractionsdecimal fractions, using his/ her own methods or by using a calculator.

Timingmdc8210c2e0bf5757_1528449068082_0Timing

45 minutes

General objectivemdc8210c2e0bf5757_1528449523725_0General objective

Performing uncomplicated calculations in memory, or in more difficult cases in a written algorithm and using these skills in practical situations.

Specific objectivesmdc8210c2e0bf5757_1528449552113_0Specific objectives

1) Subtraction of decimal fractions in memorysubtraction of decimal fractions in memory / also mental subtraction of decimal fractionsSubtraction of decimal fractions in memory (mental subtraction).

2) Subtraction of decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithmSubtraction of decimal fractions in a written algorithm.

3) Communicating in English, developing mathematical, scientific, technical and IT competences, developing learning skills.

Learning outcomesmdc8210c2e0bf5757_1528450430307_0Learning outcomes

1) Student performs uncomplicated subtraction of decimal fractions in memorysubtraction of decimal fractions in memory / also mental subtraction of decimal fractionssubtraction of decimal fractions in memory,

2) Student subtracts decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithmsubtracts decimal fractions in a written algorithm.

Methodsmdc8210c2e0bf5757_1528449534267_0Methods

1) Discussion.

2) Situational analysis.

Forms of workmdc8210c2e0bf5757_1528449514617_0Forms of work

1) Group work.

2) Individual work.

Lesson stages

Introductionmdc8210c2e0bf5757_1528450127855_0Introduction

Students review the rules and methods of adding decimal fractionsdecimal fractionsdecimal fractions.

Discussion - In which situations do we most often encounter the subtraction of decimal fractionsdecimal fractionsdecimal fractions? The teacher gives students examples of prices of sample commodities before and after price reduction.

[Table 1]

On the basis of the table, students create questions and answer them.
Examples of questions:
- How much less does a notebook cost after price reduction?
- How much has the price of the notebook been reduced?
- How much has the price of the pen been reduced?mdc8210c2e0bf5757_1527712094602_0On the basis of the table, students create questions and answer them.
Examples of questions:
- How much less does a notebook cost after price reduction?
- How much has the price of the notebook been reduced?
- How much has the price of the pen been reduced?

Discussion - How to subtract two decimal fractionsdecimal fractionsdecimal fractions?

Proceduremdc8210c2e0bf5757_1528446435040_0Procedure

Students should draw a conclusion:
- By subtracting two decimal fractionsdecimal fractionsdecimal fractions, we subtract the whole from the whole, and the fractional parts from the fractional parts, e.g.

[Illustration 1]

Task
Students calculate in memory.

a) 4.758 - 2.452

b) 12.52 - 4.20

c) 14.6 - 5.2

d) 0.825‑0.520

Task
Pupils are wondering how to subtract decimals, in which the number of digits after the decimal point is not the same. They perform calculations.

a) 3.56 - 2.5

b) 5.2 - 3.15

c) 12.54 - 2.125

Students should draw a conclusion:
To subtract fractions with a different number of digits, first expand or simplify the fractions so that the number of digits after the decimal point matches. Then perform the subtraction.mdc8210c2e0bf5757_1527752263647_0To subtract fractions with a different number of digits, first expand or simplify the fractions so that the number of digits after the decimal point matches. Then perform the subtraction.

Task
Students work individually using computers. They open the slideshow and observe how we subtract the decimal fractionsdecimal fractionsdecimal fractions in written algorithms. After completing the task, the students present the results of their observations.

[Slideshow]

Students should draw the following conclusions:
- Subtracting decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithmSubtracting decimal fractions in a written algorithm is performed in a similar way as in a written algorithm of subtraction of natural numbers.
- The numbers should be written in such a way that the commas in both numbers are lined one after the other vertically.
- We subtract the whole from the whole, the tens from the tens, the hundreds from the hundreds, etc.

Task
Students perform subtraction in a written algorithm.

a) 31.46 - 12.32

b) 16.70 - 9.74

c) 42.8 - 36.49

d) 19.4‑6.728

e) 127.28 - 14.56

Students solve word problems. They perform a written subtraction algorithm and check its correctness by adding.

Task
1. The box together with the fruit weighs 11.5 kg. How much does the fruit weigh if the empty box weighs 0.96 kg?
2. The Elbląg Canal is 62.5 km long, and the Augustowski Canal is 80 km. How many kilometers is the Elbląg Canal shorter than the Augustowski Canal?
3. In the morning there were 350,5 kg of sweets in the store, and 275,75 kg in the evening. How many kilos of candies were sold?

An extra task
Calculate, with the order of operations in mind.

a) 325.32 + 25.32 - 201.25

b) 215.65 - 26.35 + 45.32

c) 215.65 - (23.35 + 45.32)

Lesson summarymdc8210c2e0bf5757_1528450119332_0Lesson summary

Students do revision exercises.
Then they summarize the lesson together, formulating conclusions to remember:
- By subtracting decimal fractionsdecimal fractionsdecimal fractions, we subtract the whole from the whole, the tens from the tens, the hundreds from the hundreds, etc.
- Subtracting decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithmSubtracting decimal fractions in a written algorithm is performed in a similar way as a written subtraction of natural numbers.
- The numbers should be written in such a way that the commas in both numbers are lined one after the other vertically. Then we subtract the whole from the whole, the tens from the tens, the hundreds from the hundreds, etc.
- If there is a different number of digits after the decimal point, we extend or simplify the fractions, so that the number of digits after the decimal point matches.
- We check the subtraction result by adding.

Selected words and expressions used in the lesson plan

decimal fractionsdecimal fractionsdecimal fractions

hundrethshundrethshundreths

subtraction of decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithmsubtraction of decimal fractions in a written algorithm

subtraction of decimal fractions in memory / also mental subtraction of decimal fractionssubtraction of decimal fractions in memory / also mental subtraction of decimal fractionssubtraction of decimal fractions in memory / also mental subtraction of decimal fractions

tenthstenthstenths

thousandthsthousandthsthousandths

wholeswholeswholes