Lesson Page
Mathematical Reasoning

 

Writing a number sentence helps organize the information within a math problem. It's a way of showing the relationship between the known facts and the unknowns in the problem.

Example:

Phil likes to use his computer to find information on the Internet. Each hour on-line costs him $1.50. If he searches for 5 hours, what is the cost?

 

What are you asked to find?

the total cost for 5 hours of on-line time

What information will you use?

$1.50 for each hour and 5 hours of use

Is there any information you won't use?

no

What strategy can you use to find the answer?

You can write a number sentence to find the total cost of the on-line time. A number sentence can show how the facts in the problem are related.

You can write a number sentence that uses n to stand for the product.

number of hours   cost per hour   total cost of on-line time  
     
5 x $1.50 = n $1.50
x     5
$7.50
n = $7.50

So, Phil needs $7.50 to pay for the cost of his time on the Internet.

 


LOOK BACK

 

What other strategies could you have used to solve the problem?

Possible answer: Make a table

 

Problem: Nicole spent $215.75 on computer programs. Lisa spent $75.25 on computer programs. How much more did Nicole spend than Lisa?

Fact Question

Read

$215.75 (amount Nicole spent) - (minus sign) $75.25 (amount Lisa spent ) = (equal sign) n (how much more Nicole spent).

Plan

$215.75
- $75.25
$140.50

Solve

Nicole spent $140.50 more than Lisa.

  Let's Practice!
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Remember:
It is important to be able to interpret symbols when reading or writing a number sentence.

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