Operations with decimal number pt. 2

• Wiskunde
• Middelbare school
• vwo
• Leerjaar 2

Good morning!

Schedule: 

• Learning goals 
• Multiplying/dividing tricks explained
• Continue Natalica zoo 
• Investigation B/C discussion

Learning goals 

At the end of this lesson I can:

• Use operations on decimals in real life context
  
• Collaborate with other people to find a solution 
• Reflect on my previous work

The mass of a jar of sugar is 1.9 kg. What is the total mass of 13 jars of sugar?

Multiplying decimals

The mass of a jar of sugar is 1.9 kg. What is the total mass of 13 jars of sugar?

1.9 ⋅ 13 = 

Remove the decimals by multiplying 1.9 by 10: 

19 ⋅ 13 = 247.0

Divide answer by 10: 

1.9 ⋅ 13 = 24.7 kg

Why does this trick work??

Multiplying decimals

The mass of a jar of sugar is 1.9 kg. What is the total mass of 13 jars of sugar?

1.9 ⋅ 13 = 

Remove the decimals by multiplying 1.9 by 10: 

19 ⋅ 13 = 247.0

Divide answer by 10: 

1.9 ⋅ 13 = 24.7 kg

Write both 1.9 and 13 as a fractions: 

1.9 =                              13 = 

Now multiply fractions: 

1​10​​9​​=​10​​19​​

​1​​13​​

A movie ticket costs $8.25.
If Marty spent $66 on Movie tickets, how many tickets did he buy?

Dividing decimals

A movie ticket costs $8.25.  If Marty spent $66 on Movie tickets, how many tickets did he buy?

66 ÷ 8.25 =

Remove the decimals by multiplying both numbers by 100: 

6600 ÷ 825 = 8

Why does this trick work??

Why do we not divide our answer by 100? 

Dividing decimals

A movie ticket costs $8.25.  If Marty spent $66 on Movie tickets, how many tickets did he buy?

66 ÷ 8.25 =

Remove the decimals by multiplying both numbers by 100: 

6600 ÷ 825 = 8

Write 66 and 8.25 as fractions: 

66 =                        8.25 = 

Now do the calculation with fractions: 

​1​​66​​

8​100​​25​​=​100​​825​​

Dividing/multiplying decimals

Don't remember if you should divide your final answer by the amount of decimal places in the question? 

Convert the question numbers into fractions

Natalica zoo

1. Look back at your evaluation from last lesson

2. Find the Answers on ManageBac. 

3. Mark your answers, make corrections and DISCUSS what went wrong for mistakes

4. Share:

- What are you proud of from your group? 

- What could your group improve on?

Investigation discussion

1. I will go through the answer model

2. Look through the investigation and the key. 

(If you have any questions, ask someone in your group first.) 

3. If you are done looking at your investigation, complete the reflection sheet and put the investigation + reflection sheet in your portfolio. 

4. Continue with the collaboration questions! 

Among us: escape room

Go to https://forms.gle/Rh9bo7VZehaS8wge7

And find the imposter!!

- Best collaborators 

- Best Criterion C/D

Share

What went well in your group? 

What did not go well in your group?