Class 7 Maths Algebraic Expressions Finding the Value of an Expression

Finding the Value of an Expression

The value of an algebraic expression depends on the value of the variables which forms the expression.

There are many situations where we need to find the value of an expression, such as when we want to

check whether a particular value of a variable satisfies a given equation or not.

Ex: Find the values of the following expressions for x = 5.

 3x – 7

Answer:

Replace x with 5, we get

3x – 7 = 3 * 5 – 7 = 15 – 7 = 8

Ex: Calculate the following expression for x = 3 and z = 2

6z + 4x = ?

Answer: Replace x with 3 and z with 2 in the expression, we get

6z + 4x = 6 * 2 + 4 * 3 = 12 + 12 = 24

Problem: If m = 2, find the value of:

(i) m – 2                  (ii) 3m – 5             (iii) 9 – 5m               (iv) 3m2 – 2m - 7                (v) 5m/2 – 4

Answer:

Put m = 2, we get

(i) m – 2 = 2 – 2 = 0          

(ii) 3m – 5 = 3 * 2 – 5 = 6 – 5 = 1     

(iii) 9 – 5m = 9 – 5 * 2 = 9 – 10 = -1        

(iv) 3m2 – 2m – 7 = 3 * 22 – 2 * 2 - 7

                               = 3 * 4 – 4 – 7

                               = 12 – 11

                               = 1          

(v) 5m/2 – 4 = (5 * 2)/2 – 4

                       = 10/2 – 4

                       = 5 – 4

                       = 1

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