Reduce a number of times

### 1.1. Knowledge to remember

- Length of line segment AB: 8cm

Length of line segment CD: 8 : 4 = 2 (cm)

If the length of line segment AB is reduced by 4 times, the length of line segment CD will be obtained.

*To reduce a number more than once, we divide that number by the number of times.*

### 1.2. Solving textbook exercises

**Lesson 1:** Write (according to the form)

Number given | twelfth | 48 | 36 | 24 |

4 times off | 12 : 4 = 3 | |||

6x discount | 12 : 6 = 2 |

**Solution guide:**

Number given | twelfth | 48 | 36 | 24 |

4 times off | 12 : 4 = 3 | 48 : 4 = 12 | 36 : 4 = 9 | 24 : 4 = 6 |

6x discount | 12 : 6 = 2 | 48 : 6 = 8 | 36 : 6 = 6 | 24 : 6 = 4 |

**Lesson 2:** Solve the problem (according to the sample solution)

a) Mother has 40 pomelos, after selling, the number of pomelos decreases 4 times. How many grapefruits do you have left?

**Solution:**

The number of mother pomelos left is:

40 : 4 = 10 (fruit)

Answer: 10 fruits.

b) A manual job takes 30 hours, if done by machine, the time is reduced by 5 times. How many hours does it take to do the job by machine?

**Solution method**

To find the answer, we divide the time taken by hand by 5.

**Solution **

The time to do that job by machine is:

30 : 5 = 6 (hours)

Answer: 6 hours.

**Lesson 3:** Line segment AB is 8 cm long

a) Draw a line segment CD whose length is 4 times the length of line AB

b) Draw a line segment MN whose length is the length of line segment AB reduced by 4 cm.

**Solution method **

a) Find the length of line segment CD by dividing the length of line segment AB by 4.

Use a ruler to draw a line segment CD according to the length found.

b) Find the length of line segment CD by subtracting 4cm from the length of line segment AB.

Draw the line segment MN according to the length found.

**Solution **

a) First calculate the length of line segment CD:

8: 4 = 2 (cm)

Then use a straightedge with gasoline – ti – meter lines to draw a line segment CD with length 2 cm.

b) Calculate the length of the line segment MN:

8 – 4 = 4 (cm)

Draw a line segment MN 4 cm long.

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