standard_description: Identify when two expressions are equivalent (i.e., when the two expressions name the same number regardless of which value is substituted into them). For example, the expressions y + y + y and 3y are equivalent because they name the same number regardless of which number y stands for.
problem_activity: Problem 1
Sarita has a fish tank in the shape of a rectangular prism. The bottom of the fish tank measures
$${10}$$
inches by
$$8$$
inches. Sarita wants to add some sand to cover the bottom of the tank, and she uses the formula
$${ V=l × w × h}$$
to determine the volume of sand she needs.
a.   If the height of the sand measures
$$2$$
inches, what is the volume of sand needed?
b.   If the height of the sand measures
$${3.5}$$
inches, what is the volume of sand needed?
c.   Sarita cannot decide how high she wants the sand to be in the tank. What expression can she use to represent the volume of sand needed for
any
height of sand?
Problem 2
In each example, write an expression to represent the quantity.
a.   Thomas is
$$x$$
years old.
His sister is
$$5$$
years older. How old is his sister?
His dog is
$$3$$
years younger. How old is his dog?
His cousin is
$${3\over4}$$
his age. How old is his cousin?
His friend is
$$y$$
years younger. How old is his friend?
b.   Reina has
$$5$$
more quarters than dimes.
She has
$$8$$
dimes. How many quarters does she have?
She has
$$15$$
quarters. How many dimes does she have?
She has
$$d$$
dimes. How many quarters does she have?
She has
$$q$$
quarters. How many dimes does she have?
Problem 3
a.   A numeric expression like
$${5+(8+2)^2}$$
has one and only one value. What is it?
b.   Consider the expression
$${ {5+(x+2)^2}}$$
. What are some values it can have? Make sure you organize your work so anyone can tell which value for the expression goes with which
$$x$$
value.
c.   How many different values can an algebraic expression like
$${5+(x+2)^2}$$
have?


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