**Writing and Evaluating Expressions :**

In this section, we will learn, how to write a mathematical expression from a verbal description and evaluating expressions for the given values of the variables or unknowns.

Let us see, how to write verbal phrase into expressions.

If there is any unknown value, in the given verbal phrase, replace it by some English alphabet.

**Question 1 :**

Write the given verbal phrase into mathematical expression

"The sum of 5 times a number and 8"

**Answer :**

5x + 8

**Question 2 :**

Write the given verbal phrase into mathematical expression

"2 times the sum of 7 times a number and 4"

**Answer :**

2(7x + 4)

**Question 3 :**

Write the given verbal phrase into mathematical expression

"7 less than 4 times a number"

**Answer :**

4x - 7

**Question 4 :**

Write the given verbal phrase into mathematical expression

"One fifth of sum of 3 times a number and 9"

**Answer :**

(3x + 9) / 5

**Question 5 :**

Write the given verbal phrase into mathematical expression

"One seventh of 3 less than 4 times a number"

**Answer :**

(4x - 3) / 7

**Question 6 :**

Write the given verbal phrase into mathematical expression

"5 times of a number is decreased by 8"

**Answer :**

5x - 8

**Question 7 :**

Write the given verbal phrase into mathematical expression

"6 times of a number is increased by 15"

**Answer :**

6x + 15

**Question 8 :**

Write the given verbal phrase into mathematical expression

"7 less than 3 times the sum of a number and 6"

**Answer :**

3(x + 6) - 7

**Question 9 :**

Write the given verbal phrase into mathematical expression

"3 times the difference between a number and 8"

**Answer :**

3(x - 8)

**Question 10 :**

Write the given verbal phrase into mathematical expression

"One fourth of 3 times the difference between a number and 6"

**Answer :**

3(x - 6) / 4

**Question 1 :**

Evaluate the given expression for x = 3 and y = 5.

3x + 2y

**Answer :**

Plug x = 3 and y = 5 in the given expression

= 3(3) + 2(5)

= 9 + 10

= 19

Hence, the answer is 19.

**Question 2 :**

Evaluate the given expression for m = 5 and n = 2.

m² + 2mn²

**Answer :**

Plug m = 5 and n = 2 in the given expression

= 5² + 2(5)(2)²

= 25 + 40

= 65

Hence, the answer is 65.

**Question 3 :**

Evaluate the given expression for s = 5.

s² + 7s - 2

**Answer :**

Plug s = 5 in the given expression

= 5² + 7(5) - 2

= 25 + 35 - 2

= 58

Hence, the answer is 58.

**Question 4 :**

Evaluate the given expression for m = 1/3.

18m² + 3m + 7

**Answer :**

Plug m = 1/3 in the given expression

= 18(1/3)² + 3(1/3) + 7

= 2 + 1 + 7

= 10

Hence, the answer is 10.

**Question 5 :**

Evaluate the given expression for m = 13.

m² + m - 54

**Answer :**

Plug m = 13 in the given expression

= 13² + 13 -54

= 169 + 13 - 54

= 128

Hence, the answer is 128.

**Question 6 :**

Evaluate the given expression for x = 3 and y = 5.

x² + y²

**Answer :**

Plug x = 3 and y = 5 in the given expression

= 3² + 5²

= 9 + 25

= 34

Hence, the answer is 34.

**Question 7 :**

Evaluate the given expression for m = 5 and n = 2.

5m² + 2m²n

**Answer :**

Plug m = 5 and n = 2 in the given expression

= 5(5)² + 2(5)²(2)

= 125 + 100

= 225

Hence, the answer is 225.

**Question 8 :**

Evaluate the given expression for s = 6.

s² -3s + 10

**Answer :**

Plug s = 6 in the given expression

= 6² - 3(6) + 10

= 36 - 18 + 10

= 28

Hence, the answer is 28.

**Question 9 :**

Evaluate the given expression for x = 2 and y = -5.

x² - 3y²

**Answer :**

Plug x = 2 and y = -5 in the given expression

= 2² + 3(-5)²

= 4 + 75

= 79

Hence, the answer is 79.

**Question 10 :**

Evaluate the given expression for m = 3.

(2m² + 5m - 7) / 2

**Answer :**

Plug m = 3 in the given expression

= [2(3)² + 5(3) - 7] / 2

= [18 + 15 - 7 ] / 2

= 26 / 2

= 13

Hence, the answer is 13.

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