Unit 3. Decimals

Unit 3. Decimals

by MARÍA LORENZO

What do you know about decimals?​

When do we use them?​

Multiple Choice

Which of these numbers is the lowest?

• 0.425

• 0.252

• 0.415

• 0.465

Multiple Choice

Which of these numbers is the highest?

• 0.425

• 0.252

• 0.415

• 0.465

Multiple Choice

How many decimals numbers are between 1 and 2?

• Infinites

  (infinitos)

• Just one, the 1.5

  (Sólo uno y es el 1.5)

• Ten numbers:

  1,1   1,2  1,3   1,4.... 

• None 

  (ninguno)

​Reduce decimal numbers

​Round off = redondeo

​

​Examples:

​6,22336 = 6,2234

​6,22336 = 6,223

​6,22336 = 6,22

​

​7,5648 = 7,565

​7,5648 = 7,56

​7,5648 = 7,6

​Addition and subtraction

​To add and subtract decimal numbers, we put them in a column matching the corresponding decimal places.

Multiple Choice

Calculate: 

1,8 + 2,1

• 1,5

• 10,2

• 3,9

Multiple Choice

Calculate:

2,25 + 3,6

• 2,61

• 5,85

• 5,25

Multiple Choice

Calculate:

1,25 + 2 + 1,40

• 4,65

• 3,40

• 3,25

• 2,67

Multiple Choice

Calculate: 

4,21 - 3,72

• 1,51

• 0.49

• 7,93

Multiple Choice

Calculate:

5 - 3.81 =

• 1,81

• 8,81

• 1,19

Multiple Choice

Calculate:

(2,23 + 4,75) - 3,64 =

• 3,34

• 10,62

• 6,34

​Multiplication

​We multiply decimal numbers as if they are integers, then we separated in the product as many decimale places, as the sum of the decimal places of two factors.

Multiple Choice

Calculate:

2 · 3,24 =

• 5,24

• 6,48

• 3,48

Multiple Choice

Calculate:

3,21 · 2,1 =

• 5,31

• 1,11

• 67,41

• 6,741

Multiple Choice

Calculate:

4,25 · 1,72 =

• 7,31

• 5,97

• 2,53

Multiple Choice

I went shopping with 30 €, but I spent 12,50 € in a book and 7,55 € in a box of chocolates. How much money did I spend?

• 30

• 12,5

• 7,55

• 20,05

Multiple Choice

I went shopping with 30 €, but I spent 20,05 €. How much money did I have at the end of the day?

• 30

• 9,95

• 9,05

• 20,05