WRITING AND EVALUATING EXPRESSIONS
About "Writing and evaluating expressions"
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.
Writing Expression from a Verbal Phrase
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.
Example 1
Example 2
Example 3
Writing Expressions - Practice Questions
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
Evaluating Expressions - Practice Questions
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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