 # 1 - Adding and subtracting

1 - Adding without carrying

We have already seen the simple additions, now let us see how to add large numbers easily. To calculate easily 1245+3541, first you have to place the two numbers one below the other ligning up the units numbers, you write the symbol + and you draw a line below the two numbers. Then you add the units numbers. 5+1=6 so you write down 6 below the line. You do the same with the tens numbers. 4+4=8 so you write 8 below the line. You do the same with the hundreds numbers. 2+5=7 so you write 7 below the line. Finally, you add the thousands numbers. 1+3=4 so you write 4 below the line. This way you can now read the result below the line : 1245+3541=4786.

Train yourself!
Use this method to answer the following question :
What is the value of 459 + 300 ?

2 - Adding and carrying

Sometimes, when adding two numbers of a same column, you find a result larger than 10. For example with the addition 2455+1927, 5+7=12 In this case, do not write 12 below the line but only 2, and the 1 is written on the top of the column on the left. It is called carrying and you then have to add it with the tens column. Now you add the tens column, with the number you carried, 1+5+2=8 so you write 8 below the line. Then you add the hundreds numbers, since you get a number bigger than 10, you write 3 below the line and you carry the proper number : Finally, you add the thousands column without forgetting the number you carried. You can conclude that 2455+1927=4382. Go on training yourself!
Use this method to answer the following question :
What is the value of 636 + 164 ?

Now that you know how to add, let's learn how to subtract.

## Subtraction

1 - Subtraction without carrying

To calculate a complicated subtraction, you start as you do with when adding : you write down the two numbers one below the other, ligning up the numbers of unities, but also writing the biggest number before. We calculate 476-145. Start with the units column. Count how many you need to get from the number below to the number on the top. Here, from 5 to 6 you need 1 so you have to write 1 below the line. Then you do the same for the tens column : from 4 to 7 you need 3 so you write a 3 below the line. Finally for the hundreds column, from 1 to 4 you need 3 so you write the number 3 below the line. You can read the final result of the subtraction: 476-145=331. To train yourself
Use this method to answer the following question :
What is the value of 427 - 220 ?

2 - Subtracting and carrying

Sometimes, in a column, the number on top is smaller than the one below. For example, for 752-318 you should start, for the units column, with calculating "from 8 to get to 2". It is not possible. When you are in this situation, you add 1 before the number on top, and 1 on the right of the number below in the column on the left. Next, you count "from 8 to get to 12". The result is 4 so you write 4 below the line. For the tens column you cannot count "from 1 to 5" as you have to add to 1 the number you have just carried over. So you count "from 2 to 5". The result is 3, so you place a 3 below the line. Finally, for the hundreds column, you count "from 3 to get to 7". The result is 4 so you place the number 4 below the line and you can read the final result of the subtraction : 752-318=434. Go on training yourself!
Use this method to answer the following question :
What is the value of 373 - 174 ?

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