how can i teach subtraction of two numbers like-456-159?

Answer 1

I view subtraction as addition.

So, -456 - 159 can be written as:
-456 + (-159)

Since it's easier to see the numbers (in my mind, anyway), you view the addition of two negative numbers and easily can add them up to -615.

When dealing with negatives, I like to simplify the equation a bit so that I have as many additions as possible, converting numbers to negative where necessary.

This is messy:
17 - (2 - 1) - (4 - 20)
But it is easier to work with if you rewrite it as:
17 + (-2) + 1 + (-4) + 20
It should result in less errors.

Answer 2

Subtraction
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"5 - 2 = 3"
An example problemSubtraction is one of the four basic arithmetic operations; it is essentially the opposite of addition. Subtraction is denoted by an minus sign in infix notation.

The traditional names for the parts of the formula

c − b = a
are minuend (c) − subtrahend (b) = difference (a). The words "minuend" and "subtrahend" are virtually absent from modern usage; Linderholm charges "This terminology is of no use whatsoever."[1] However, "difference" is very common.

Subtraction is used to model several closely related processes:

From a given collection, take away (subtract) a given number of objects.
Combine a given measurement with an opposite measurement, such as a movement right followed by a movement left, or a deposit and a withdrawal.
Compare two objects to find their difference. For example, the difference between $800 and $600 is $800 − $600 = $200.
In mathematics, it is often useful to view or even define subtraction as a kind of addition, the addition of the opposite. We can view 7 − 3 = 4 as the sum of two terms: seven and negative three. This perspective allows us to apply to subtraction all of the familiar rules and nomenclature of addition. Subtraction is not associative or commutative— in fact, it is anticommutative— but addition of signed numbers is both.


subtraction is another form of addition
the number to be subracted is known as subtrahend and the number from which it has to be subtracted is known as the minuend.
the rule for subtraction is change the sign of the number to be subtracted and add it to the minuend
example
if you want to subtract 3 from 8 change the sign of 3 and add it to 8 i.e. (-3)+8=+5
if -4 is to be subtracted from 9 it is -(-4)+9=+4+9=13
if 5 is to be subtracted from -7 it is (-5)+(-7)=-12
if -2 is to be subtracted from-6 it is -(-2)+(-6)=-8
i have explained all the four possibilities with small numbers.once the principle is understood then the children can be given larger numbers
here the sum is not clear.if -456 is to be subtracted from -159,as pe the rule it is -(-456)+(-159)=456+(-159)=456-159=297
on the other hand if -159 is to be subtracted from -456 then as per the rule it will be -(-159)+(-456)=159-456=-(456-159)=-297

Answer 3

Break out a number line. That's the way I began understanding it.

Make a number line.

One that has a middle zero, then negatives down to the answer of the subtraction problem, or a little further (Ex. in -7 - 9, the last negative number on the line could be -20). You can make it in incriments of 5, but make sure that you put in the little tick marks that make one. Just don't label each 1, just the 5's all the way down. Then, put on some positives, even though you aren't working with them, because you may need to use them to help later.

Make it big, like on posterboard.

Then, make some sort of thing that will stick to the number line easily. Like, if you have a chalkboard, which I believe are magnetic, tape the number line across the board and use large magnets as your markers.

First, make sure the kids know that when you subtract, you move left, when you add, you move right. You can demonstrate this with the few positives you stick on the right of the zero.

For example, say "If I start at 5 and I want to subtract 2, I move left 2 space and end up on 3. You all know that 5 minus 2 is 3, right? Let's move on to a harder subtraction."

Then, stick a magnet where the first number in the subtraction problem falls. Let's use -10 - 5. Stick one magnet at the -10. Then, show the movement left 5 tick marks, because you are subtracting 5. Make sure to remind them you are moving left. Show them, that now you end up on -15. Put another magnet there. Do this with many, many examples.

Allow children to ask questions.

Keep the number line up there, free of magnets, so while you are practicing with them, they can look up and visualize it to themselves. Pretty soon, they will realize that you are really just adding the two numbers and keeping the negative in front.

After a while of the number line, you can try to show them, that an easy way to remember is to add the numbers and stick the negative out front.

It is just more educational if you use the number line first, to show them WHY it SEEMS like they are getting a bigger number.

Answer 4

The first way I approach teaching adding and subtracting positives and negatives is to deal with the first number as a bank balance and the second as income or a bill. (Kids seem to understand money, for some reason!)

With -456 - 159, teach the kids they're in debt $456, and another bill comes in for $159. How much do they now owe?

In dealing with subtracting a negative, it's a bank error... finding a bill that wasn't supposed to be charged to their account:
-290 - (-338) means a balance of -$290, they're subtracting a bill that was charged for $338, meaning it's $338 in their favor.
-290 - (-338) = -290 + 338 = 48. The student has a $48 balance.

Answer 5

-456 is already 456 points to the negetive of 0. If you want to subtract 159 from it, you will be dragging it further negetive to another 159 points, which is (456+159) to the left. That is 615 negetive, so -615

Answer 6

Say , 456 negatives and 159 negatives make?

The +(-456) crap is confusing and wrong as it takes the equation back a step. NOBODY does that in countries that actualy score well in world competitions.

Answer 7

I treat it like this:
Suppose you are on the ground floor of an apartment and identify it with 0. The first floor is 1, the second 2 and so on. Similarly as you go in the basement you are on -1, further 1 floor down(if that's possible) is -2 and so on. So -2-3 is just that first u went 2 storeys underground and then went a further 3 storeys underground. So you ended up at 5 underground i.e. at -5.
In this way we can also consider combinations of positive and negative numbers -2 + 3 =1 and so on.

Answer 8

First of all assume that when you get money it is positive and when you pay it is negative.
First of all you pay me $456 and again pay me more $159 then check how many dollars yo have paid me. You will find that in total you have paid me $615. The answer is $615, but you have paid therefore it will have negative sign.

Answer 9

Start by teaching 16 - 9

Answer 10

Simpler method:-

(i) 450 - 150 = 300 (ii) 6 - 9 = -3 (iii) 300 - 3 =297