Introducing the pocket calculator

### 1.1. Knowledge to remember

**a)** Description of pocket calculator

The pocket calculator helps us to perform commonly used calculations such as addition, subtraction, multiplication, division and problem solving with percentages.

There are many types of pocket calculators. Basically the types of pocket calculators and how to use them are similar. For example, a computer has a surface as shown below:

In addition to the screen, we see the following keys:

– On/c key to turn on the device.

– Off key to turn off the device.

– Number keys from 0 to 9 to enter numbers.

– Compound keys for addition, subtraction, multiplication, division: +, -, x, :

– Keys. to put commas in decimals

– Key = to display calculation results on the screen.

– CE key to delete the number entered if incorrect.

– Other special keys: R-CM, CODE^{–}, USA^{+}, , %, ^{+}//

**b)** Perform calculations using a pocket calculator.

– To operate the machine, need to press the ON/OFF key

– To calculate 25.3 + 7.09 we press the following keys in turn:

2 5 . 3 + 7 . 0 9 =

– On the screen appears the result 32.29, ie 32.29

To perform calculations, subtraction, multiplication, and division we do the same.

### 1.2. Solve textbook exercises page 82

**Lesson 1 of the textbook page 82: **

Do the following calculations and then check the results with a calculator:

a) 126.45 + 796,892; b) 352.19 – 189,471;

c) 75.54 x 39; d) 308.85 : 14.5.

*Solution guide:*

Press the buttons in turn:

a) 1 2 6 . 4 5 + 7 9 6 . 8 9 2 =

Answer: 923,342

b) 3 5 2 . 1 9 – 1 8 9 . 4 7 1 =

Answer: 162.719

c) 7 5 . 5 4 x 3 9 =

Answer: 2946.06

d) 3 0 8 . 8 5 : 1 4 . 5 =

Answer: 21.3

Lesson 2 Textbook page 82:

Write the following fractions in decimal (use a calculator)

\(\frac{3}{4};\frac{5}{8};\frac{6}{{25}};\frac{5}{{40}}\])

*Solution guide:*

Divide the numerator by the denominator:

– Press 3: 4 =

On the screen appears the result 0.75, ie 0.75.

So: \(\frac{3}{4}\)=0.75

– Press 5: 8 =

On the screen appears the result 0.625, ie 0.625.

So: \(\frac{5}{8}\) = 0.625

– Press 6: 2 5 =

On the screen appears the result 0.24 , ie 0.24.

So: \(\frac{6}{25}\) = 0.24

– Press 5: 4 0 =

On the screen appears the result 0.125, ie 0.125.

So: \(\frac{5}{40}\) = 0.125

Lesson 3 Textbook page 82:

One student presses the following keys in turn:

In your opinion, what expression value did that friend calculate?

*Solution guide:*

That friend will receive the value of the expression: 4.5 × 6 – 7.

The result of the expression is: 4.5 × 6 – 7 = 20.

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