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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.


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?


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
n = $7.50

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




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


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


- $75.25


Nicole spent $140.50 more than Lisa.

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It is important to be able to interpret symbols when reading or writing a number sentence.

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