IXL | Add and subtract integers: word problems

Read this word problem.

A trout was swimming 9 feet below the surface of a lake. It dove down 8 more feet to search for food. What is the position of the trout now relative to the surface?

To solve the problem, Denise subtracted

–

and came up with an answer of

–

feet. Is Denise correct? Why or why not?

Yes, Denise is correct.

No. The answer should have been 17 feet, not

–

feet, because a negative plus a negative is always a positive.

No. Denise should have subtracted

–

because she needed to find the difference in the trout's starting and ending position.

ref_doc_title.

Learn with an example

question

Read this word problem.

Kayla began a science experiment with 18 grams of an unknown solid. During the experiment, the change in the mass of the solid was

–

grams. What was the mass of the solid at the end of the experiment?

To solve the problem, Edna subtracted

–

(

–

)

and came up with an answer of 25 grams. Is Edna correct? Why or why not?

Yes, Edna is correct.

No. The answer should have been

–

grams, not 25 grams, because the mass of the solid decreased.

No. Edna should have added

(

–

)

because she needed to add the initial mass and the change in mass.

key idea

To add two numbers with the same

sign,

add the absolute values of the numbers. Keep their sign. For example,

–

(

–

)

–

To add two numbers with different

signs,

subtract the absolute values of the numbers. Keep the sign of the number with the larger absolute value. For example,

–

Subtracting a number is the same as adding its opposite. For example,

–

(

–

)

–

solution

To see if Edna is correct, start by listing the information she was given in the problem.

The mass of the solid was 18 grams.
The change in the mass of the solid was
–
7
grams.

Now write an expression that represents the situation. Edna needs to find the final mass, so she needs to add.

18	+	( – 7 )	=	?

initial mass		change in mass		final mass

Add.

(

–

)

So, the mass of the solid at the end of the experiment was 11 grams.

Edna is

incorrect.

Edna should have added 18 + (-7) because she needed to add the initial mass and the change in mass.

Looking for more? Try these:

Lesson: Adding and subtracting integers

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A.4Add and subtract integers

A.1Understanding integers

Lesson: Adding and subtracting integers

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