I still can't figure out adding and subtracting negative and positive numbers together!!!!?

Question

I know it sounds silly, and I SHOULD be able to do this by 8th grade but I just can't understand how to do it!!!! I have a test tommorow in math and we can't use calculators, I'm really starting to panic! What are some easy ways to remember the rules that I can understand?

Answer 1

Think of it this way: You're counting numbers above and below zero.

Here's a math problem:

-10 + 5 = ?

Picture a thermometer. You go down 10 degrees below zero, then you add 5 degrees (so you go up). The answer is

-10 + 5 = -5

If the larger number is negative, the answer will always be a negative number. If the larger number is positive, the answer will always be positive.

Suppose you have two negative numbers.

-10 plus -10 =

You go 10 degrees below zero, then subtract 10 more.

A couple of other things. If you're multiplying a negative number times a positive number, the answer will always be negative.

-10 x 10 = -100

And so on.

Just think of a thermometer and you'll do fine.

Answer 2

Ok, the rules are as follows (adding and subtracting)

- adding two positive numbers = result is always positive

- adding two negative numbers = add the numbers like you will normally do in the positive number case...and insert the negative sign at the end.

example: -5 + -12 = -(5+12) = -17

- adding one positive and one negative: subtract one number from the other; the sign will be determined by the absolute value of the larger number.

Example: -5 + 12 = (12-5) = 7
Note that positive 12 has the larger magnitude of the two numbers (12 and 5)

Example: 5 + -12 = -(12-5) = -7 Note that this time the largest number (12) is a negative number; thus, the result is negative.

Subtraction:

two positive numbers: watch for the first one being larger than the second one...in this case, the result of the subtraction is positive.

example: 5-3 = 2
3-5 = -1 Note that 3 is smaller than 5

two negative numbers:

example" -5-(-7) = -5 + 7 = 2

Mix case:

example: -5-8 = -(5+8) = -13


Hope this explanation helps you tomorrow. Just practice, practice, practice.

Answer 3

When you're adding a combination of positive and negative numbers,
here's what helps me.

I think of a positive number as going a distance to the right. For
instance, if you start like:

............x............

then 4 would be:

............!...x........

See how you've moved to the right 4 places. The ! is where you started
from.

I think of a negative number as going to the left. For instance, if we
go back to the starting point:

............x............

what would a -7 look like?

.....x......!............

Okay? It's seven places to the left.

Now, when you want to add two positive numbers, you just add them.
4 + 6 is where you'd end up if you first went 4, and then went 6 more,
which is at 10.

When you want to add two negatives, like (-4) + (-6), it's like going 4
to the left, and then another 6 to the left, you end up at -10.

So, adding two negatives is just as easy as adding two positives. Just
add them, but remember that the answer is negative. So your first
problem is not hard at all since you're adding a negative 31 and a
negative 46. Go for it.

What about combinations of positives and negatives?

This is the only interesting situation. Both the remaining problems
are of this type. What happens?

What happens if you add -8 and a 12? One number takes you one
direction, and the other number takes you in the other. You can easily
see that you end up a distance of 4 from where you started. On which
side? It depends on which number was bigger. If the negative number was
bigger, it wins, and you wind up on the left. If the positive number
is bigger, *it* wins, and you wind up on the right!

In the case of -8 + 12, who wins? The 12, so you only go a distance of
4 (the difference between the numebrs), and since 12 is bigger, it's
on the right. The answer is 4.

How about 56 + (-61)? Here the -61 wins against the 56. The difference
is 5. Answer: -5.

What about (-98) + 108? Answer: 10.

Hope this helps!

- Doctor Santu, The Math Forum
http://mathforum.org/dr.math/

Answer 4

Think of it as all addition. Subtraction is just the addition of negative numbers:

9-6=3 and 9+ (-6)=3 also.

The only trick then becomes subtracting a negative number:

14-(-9)=23 is the same as 14+9=23

When you subtract a negative number, the signs become positive.

12-(-3)=15
72-(-8)=80
0-(-1)=1

The only rule that is really necessary is that one. Otherwise add everything together.

Another good math rule in general is to stay calm. You can get this.

Answer 5

One device I've used with folks having trouble conceptualizing combining positive and negative numbers is the number line. You can do a web search on it and read more detail but here is a start. draw a line on a sheet of paper and in the middle mark a zero. Equally space the integers 1 through 10 to the right of zero and negative 1 through 10 to the left of zero. Now you simply count out your answer. For instance: in the example positive 6 plus negative 3 you could put you finger on negative 3 and count six integers to the right. Good luck. Sometimes visual aids make all the difference.

Answer 6

p=positive
n=negative

p+p=p 2 + 2 = 4
n+n=n -2 + -2 = -4

p+n=take the sign of the bigger number and then subtract
25 + -47 = -

47
-25
___
22

25 + -47 = -22
Theres your adding part now to the subtraction.
p - p =?
When subtracting remember that the normal way is that the bigger number is first.But in this case it can be either way.
5 - 2 = 3
2 - 5 = -3
My teacher told us to change the subtraction sign to a addition and make the second number it's opposite.
2 - 5
2 +(-5)= 3
If you get the addition memorized then remember this and it will be eeeeaasssyyy.


Oh yeah, and if you thought this was good teaching then print this out and ask your teacher if you can use notes.But,i would memorize this first just incase your teacher says no.

Answer 7

-4 + 6 is notably plenty basically 6 - 4. The (-) is often tied to the variety, so in case you turn 4 and 6 it wouldnt be -6 + 4 yet 6 - 4. -a million - (-4) is a double unfavourable. in case you're ever subtracting a unfavourable variety you regulate it to a plus. it might exchange into -a million + 4. -40 5 - 12 + 37. The -40 5 - 12 is basically -40 5 + (-12) so - 57. -57 + 37 is basically 37 - 57, so -20.

Answer 8

sometimes it's easier to make a line, like...

-5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5

add positive numbers to the right +3 plus +2 equals +5

subtract positive numbers to the left +5 minus +2 equals +3

add 2 negative numbers to the left -2 plus -3 equals -5

if you have positive and negative it is as follows -2 plus +3 equals +1 Start at the negative 2 on the line and move three spots to the right.

Hope this helps

Answer 9

to add a positive number to a negative number you subtract the negative number from the positive

ex. -3 + 5 = 2
ex. -27 + 30 = 3

Answer 10

If the signs are different, subtract and give the answer the sign of the largest number. ex -4 + 7 = 3 if the signs are alike add the numbers and give the answer the same sign ex -4 + -7 = -11