Question

Alaina gained m dollars in the stock market two weeks ago. Last week, she gained twice as much. This week, she lost $50 more than she gained the first week. How do you write an algebraic expression for her total gain or loss?

Answer 1

To evaluate a variable expression means to find the value of the expression when the variable is (or variables are) replaced by a number (or numbers).

Here is a variable expression:

3

x

+

7

.

To evaluate this expression when

x

=

2

mean to substitute

2

in place of

x

, and find the number (the value). [see note below]

3

(

2

)

+

7

=

6

+

7

=

13

.

When

x

=

2

, the expression has a value of `

13

.

If we evaluate the same expression when

x

=

10

, we get:

3

(

10

)

+

7

=

30

+

7

=

37

.

Here's a variable expression with two variables :

3

x

−

2

y

In order to evaluate this expression, we'll need values (numbers) for both

x

and

y

.

Evaluate the expression

3

x

−

2

y

when

x

=

4

and

y

=

5

3

(

4

)

−

2

(

5

)

=

12

−

10

=

2

If we change the values to

x

=

5

and

y

=

4

, we get

3

(

5

)

−

2

(

4

)

=

15

−

8

=

7

.