3.2+Subtracting+on+a+Number+Line+0910

April 19 2010

A.S

Big Idea: Negative numbers help us to model many real world situations.

Essential Question: How do I find the difference between integers?


 * 3.2 & Follow Up

A. Use the number line to find each difference. Use a chipboard to check your work.

1.** +7-+9= -3
 * 2.** -7-+9= -16
 * 3.** +7--9= 16
 * 4.** -7--9= 3


 * B. Use a number line to find each sum or difference.**


 * 1.** +12-+3= 8
 * 2.** +12+-3= 15
 * 3.** -10--7= -17
 * 4.** -10++7= -17


 * C. Find the difference between each pair of numbers on a number line. In each case, tell how the distance is related to the difference is related to the difference between the two numbers.**


 * 1.** 1 and 5 are positive integers so we need to look at the right side of the number line to count the difference. The difference is 4.
 * 2.** -1 and 5 are integers with different signs so we cannot look at just the left side or the right so we look at the greater number 5. 5 is a positive number and is greater than -1 so we count the differnce going from left to right. The difference is 6.
 * 3.** -5 and -9 are negative numbers so we look at the left side of the number line to count the difference. The difference is 4.
 * 4.** -3 and 3 are opposites so the difference will be the the numbers absolute value multiplied by 2. The difference is 6.
 * D) Write two number sentences illustrated by this figure.**

My 2 sentences are +5 - 7=-2 and 0+5-7=-2.


 * 3.2 Follow Up**


 * 1.** **When you add two positive integers you get a positive sum . When you subtract two positive integers, do you always get a positive difference? Explain.**

No. It can be possible to get a negative number if a number is trying to subtract a number more than it's on value.


 * 2. When you use the number line model, you can think of the //absolute value// of a number as its distance from 0. For example, 3 and -3 are each 3 units from 0, so the absolute value of each number is 3.**

a. 10 and -10 b. 5 and -5 c. 1 and -1 d. 7 and -7