Expressions containing a letter

### 1.1. Knowledge to remember

**For example:** Lan has three notebooks, Lan’s mother gives more … notebooks. Lan has all… the book

Have |
More |
Have everything |

3 3 3 … 3 |
first 2 3 … a |
3 + 1 3 + 2 3+ 3 … 3 + a |

3 + a is *expression containing a letter*

- If a = 1 then 3 + a = 3 + 1 = 4; 4 is the value of the expression 3 + a
- If a = 2 then 3 + a = 3 + 2 = 5; 5 is the value of the expression 3 + a
- If a = 3 then 3 + a = 3 + 3 = 6; 6 is the value of the expression 3 + a

*Each time we replace the digit a with a number, we get a value of the expression 3 + a*

### 1.2. Solving Textbook Exercises

**Lesson 1: **Calculate expression value (by pattern)

a) 6 – b with b = 4;

b) 115 – c with c = 7;

c) a + 80 with a = 15.

*Form: * a) If b = 4 then 6 – b = 6 – 4 = 2.

**Solution guide:**

Replace the value of the word in the expression and then calculate the value of that expression.

b) If c = 7, then 115 – c = 115 – 7 = 108 ;

c) If a = 15 then a + 80 = 15 + 80 = 95.

**Lesson 2:** Write in the blank (according to the form)

a)

x |
8 |
30 |
100 |

125 + x |
125 + 8 = 133 |

b)

y |
200 |
960 |
1350 |

y – 20 |

__Solution guide:__

- Substitute the value of the word into the expression and then calculate the value of that expression.

a)

x |
8 |
30 |
100 |

125 + x |
125 + 8 = 133 |
125 + 30 = 155 |
125 + 100 = 225 |

b)

y |
200 |
960 |
1350 |

y – 20 |
200 – 20 =180 |
960 – 20 = 940 |
1350 – 20 = 1330 |

**Lesson 3: **

a) Calculate the expression value: 250 + m with: m = 10; m = 0; m = 80; m = 30.

b) Calculate the expression value: 873 – n with: n = 10; n = 0; n = 70; n = 30.

__Solution guide:__

a) If m = 10 then 250 + m = 250 + 10 = 260.

If m = 0 then 250 + m = 250 + 0 = 250.

If m = 80 then 250 + m = 250 + 80 = 330.

If m = 30 then 250 + m = 250 + 30 = 280.

b) If n = 10 then 873 – n = 873 – 10 = 863.

If n = 0 then 873 – n = 873 – 0 = 873.

If n = 70 then 873 – n = 873 – 70 = 803.

If n = 30 then 873 – n = 873 – 30 = 573.

.

=====

## Leave a Reply