Ask a question

how do you use a number line to do -1.3-(-2.4)?

tHIS Is in a winter mathpacket. It says to use a number line to solve this promblem and to consider it.

2 Answers by Expert Tutors

Tutors, sign in to answer this question.
Rizul N. | UNC-CH Grad For Math and Science TutorUNC-CH Grad For Math and Science Tutor
4.8 4.8 (12 lesson ratings) (12)

* Note you don't have to read the green portions. They are optional.


Step 1: Put your index finger on 0. 


Step 2: The first number in the equation is -1.3 so you know you're counting 1.3 but on the left hand side where all the negative numbers exist. -1.3 is highlighted in orange.


                                               ^       <---

Step 3: Before you tackle the next number remember that you are subtracting -2.4 from -1.3 and whenever -1.3 - (-2.4) happens, it means you are adding. So whenever there are two negatives next to each other, you just make them positive. 

              -1.3 - (-2.4) becomes -1.3 + 2.4

Why? If I had -1.3 dollars, I owe Jack 1.3 dollars because it is negative. Now let's say out of that debt Jack realizes that he owes me money also and this amout was 2.4 dollars (which is essentially -2.4). He chooses to pay back some of this 2.4 dollars debt by subtracting his debt from my debt that I owe him (-1.3 dollars). The answer that I would receive back would be positive because I know that my 1.3 dollars is smaller than what he owes me so in the end I would be receiving some amount of money to put in my pocket after Jack forgive my debt to him by taking this debt out of his debt to me. 

Step 4: Now that we have just one sign to work with for 2.4, we know that because we are adding (+), we go to the right of -1.3 and add 2 first (the whole number) before doing anything with 0.4 value that comes with 2.4


                                             ---->                       ^

Step 5: Finally, count 0.4 to the right and you have your answer. 



Answer is 1.1 from the number line. 



This reply is absolutely spot on. I love your visuals. As a tutor, I am impressed!

Amen (and Merry Christmas!)!

Thank you so much guys. I am a highly visual person myself so it's definitely helpful to have a picture. Merry Christmas and a Happy New Years to you all!

As a visual learner and as a tutor, I too am highly impressed with your explanation! Thumbs up for you =)

John R. | John R: Math, Science, and History TeacherJohn R: Math, Science, and History Teach...
4.6 4.6 (55 lesson ratings) (55)

In order to use a number line to solve a problem, beging by locating the first number on the number line. Since your first number is -1.3, you will want to find the number that is 1.3 place from zero on the left.

Once you have found your starting point, find the amount of distance that the second number tells you to go.  In this case, you need to go -2.4 places.  That means you are going to find the length that is 2.4.

Since you are subtracting, you need to reverse the direction.  This means that you will go 2.4 to right, since you were originally supposed to go to the left.

Going 2.4 places to the right from -1.3 brings you to the point 1.1.

What you will find is that subtracting -2.4 is the same as adding 2.4.