SOLVING MULTI STEP PROBLEMS

Paying attention to the units used in a real-world situation can help us to solve multi step problems.

Example 1 :

The classroom aquarium holds 30 gallons of water. It is 0.8 feet wide and has a height of 2 feet. Find the length of the aquarium. Use the fact that one cubic foot of water contains about 7.5 gallons of water.

Solution : 

From the given information, we have

Step 1 : 

Find the volume of the classroom aquarium in cubic feet.

That is, 

=  30 gallons / 7.5 gallons per cubic foot

 =  4 cubic feet

(There are 7.5 gallons in 1 cubic foot. Divide to find how many groups of 7.5 gallons are in 30 gallons)

Step 2 :

Find the length of the aquarium.

Use the formula V = lwh to write an equation.

4  =  l x 0.8 x 2

4  =  l x 1.6

Divide both sides of the equations by 1.6

4/1.6  =  (l x 1.6) / 1.6

2.5  =  l

So, the length of aquarium is 2.5 feet.

Example 2 :

An aquarium holds 33.75 gallons of water. It has a length of 2 feet and a height of 1.5 feet. What is the width of the aquarium ?

(Use the fact that one cubic foot of water contains about 7.5 gallons of water.)

Solution : 

From the given information, we have

Step 1 : 

Find the volume of the classroom aquarium in cubic feet.

That is, 

=  33.75 gallons / 7.5 gallons per cubic foot

 =  4.5 cubic feet

(There are 7.5 gallons in 1 cubic foot. Divide to find how many groups of 7.5 gallons are in 33.75 gallons)

Step 2 :

Find the width of the aquarium.

Use the formula V = lwh to write an equation.

4.5  =  2 x w x 1.5

4.5  =  3 x w

Divide both sides of the equations by 3

4.5/3  =  (3 x w) / 3

1.5  =  w

So, the width of aquarium is 1.5 feet.

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