Use a calculator to help with percentages

### 1.1. Knowledge to remember

**a)** __Example 1__: Calculate the percentage of 7 and 40

– Press the keys in turn: 7 : 4 0 =

– On the screen appears the result 0.175

– Calculator:

7: 40 = 0.175

So: 7: 40 = 0.175 = 17.5%

**Attention:** The keys can be pressed in turn: 7 : 4 0 %

When the screen appears the number 17.5, this is the result 17.5%

**b)** __Example 2__: Calculates 34% of 56

– Press the keys in turn: 5 6 x 3 4 %

– On the screen appears the result 19.04

– Refined calculator: 56 x 34% = 56 x 34 : 100 = 19.04

So: 34% of 56 is 19.04

**c) ** __Example 3__: Find a number whose 65% is 78

– Turn the keys 7 8 : 6 5 %

– On the screen appears the result 120

– Calculator: 78 : 65% = 78 : 65 x 100 = 120

So: The number to find is 120

### 1.2. Solve exercises on pages 83, 84

**Lesson 1 of the textbook page 83:**

In the following table, the last column shows the percentage of girls and the total number of students in a school. Use a calculator to calculate and write the results in that column.

School | Number of students | Number of female students |
The percentage of female students and total number of students |

Honey | 612 | 311 | |

An Hai | 578 | 294 | |

An Duong | 714 | 356 | |

An Son | 807 | 400 |

*Solution guide:*

Press the following buttons in turn:

3 1 1 : 6 1 2 = (get 0.5081 = 50.81%)

2 9 4 : 5 7 8 = (get 0.5086 = 50.86%)

3 5 6 : 7 1 4 = (get 0.4985 = 49.85%)

4 0 0 : 8 0 7 = (get 0.4956 = 49.56%)

We get the following table of results:

School | Number of students | Number of female students |
The percentage of female students and total number of students |

Honey | 612 | 311 | 50.81% |

An Hai | 578 | 294 | 50.86% |

An Duong | 714 | 356 | 49.85% |

An Son | 807 | 400 | 49.56% |

Lesson 2 Textbook page 84:

On average, milling 1 quintal of rice yields 69kg of rice, which is the percentage of rice and paddy is 69%. Using a calculator, calculate the amount of rice obtained from milling and write in the blanks (in the form):

Paddy (kg) | Rice (kg) |

100 | 69 |

150 | |

125 | |

110 | |

88 |

*Solution guide:*

Using a pocket calculator we get the following results:

Paddy (kg) | Rice (kg) |

100 | 69 |

150 | 103.5 |

125 | 86.25 |

110 | 75.9 |

88 | 60.72 |

Lesson 3 Textbook page 84:

With a savings interest rate of 0.6% a month, how much money should be deposited in order to receive an interest after one month:

a) 30 000 VND;

b) 60 000 VND;

c) 90 000 VND.

(Use pocket calculator to calculate)

*Solution guide:*

Press the buttons in turn:

a) 3 0 0 0 0 : 0 . 6% =

On the screen appears the result 5 0 0 0 0 0 0.

So the amount to deposit is 5 000 000 VND.

b) 6 0 0 0 0 : 0 . 6% =

On the screen appears the result 1 0 0 0 0 0 0 0.

So the amount to deposit is 10 000 000 VND.

c) 9 0 0 0 0 : 0 . 6% =

On the screen appears the result 1 5 0 0 0 0 0 0.

So the amount to deposit is 15 000 000 VND.

.

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### Related posts:

- Introducing the pocket calculator
- Solve problems about percentages
- Percentage
- Divide a decimal by a decimal
- Divide a natural number by a decimal
- Divide a natural number by a natural number whose quotient is a decimal
- Divide a decimal by 10,100,1000..
- Divide a decimal by a natural number
- Multiply a decimal by 10, 100, 1000,..

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