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Math - Understanding SubtractionThe opposite of adding things together. In subtraction you start with one number and you take out some in that group to get a smaller number. For instance, if you were given your allowance and went to the toy store, you start off with $25. You see a game for $5, a video game for $14, and a book for $3. To find out if you have enough money to pay for all this, you can subtract $5 from the $25 to end up with $20 the take away $14 to end up with $6 and finally take away $3 which will leave you with $3 leftover in your pocket, a safe amount to get through checkout. Subtraction is an everyday fact from keeping up your budget and money management to counting down how you use your time. Even the basic jobs require knowledge of subtraction on duty, not to mention you need this skill in order to handle your paycheck. The easy way to subtract numbers is to place the higher number over the lower number guided by their numeric value as such:
In the above example, we are doing the problem 987 - 320. Notice how I place the numbers directly over each other. The higher number is place above the lower number and lined up over the lower number according to hundreds, tens and ones. This makes it easier to subtract by taking it one row at a time. Always start from the lowest value on the right which is the ones column. In this example we have 7 - 0 which equals 7. So you would put the 7 below in your ones column for your answer. The next row is the tens column where you have 8 - 2 which equals 6. You would put 6 below in the tens column for your answer. The next row is the hundreds column where you have 9 - 3 which equals 6. You would put the number 6 below in the hundreds column for your answer. The answer to the problem 987 - 320 = 667
Unfortunately, not all subtraction problems will be that easy because the numbers on the top row are smaller than the ones on the bottom. If you subtract a larger number from a smaller number, it will result in a negative number. To do these types of subtraction problems, you cannot have a negative number at the bottom. In order to get a positive number, you have to borrow 1 from the next column to the left to result in a higher number. Basically, you are adding 10 to the top number so you can subtract easily. Once you have borrowed 1 from the next column, that column no longer owns that 1 you borrowed. This means that column is minus 1 of the number you see. If the number there was 9 and you already borrowed 1, the new number is 8. If you borrowed a number and it results in a smaller number than the bottom number, you will have to borrow 1 from the next column to make that number 10+ the number which needs help. If you had a number 2 and needed to borrow a 1 from the next column, you turn the 2 into a 12 [10 + 2 = 12]. The example below shows you how the borrowing process works:
In the above example is taking 896 from 9,521. Let's say you had a large paycheck for $9,521. Rent is due and costs $896. You have other expenses and want to know how much money you will have left after you pay the rent. By placing the numbers over each other, it allows you to easily subtract the numbers in similar groupings. Always start from the right to the left. In this example you would start by subtracting the ones column. Since 1 - 6 would result in a negative number, you need to borrow a ten value number from the tens column. As you cannot subtract 1 - 6, you can subtract 11 - 6 when you borrow from the next column making it equal to 10 + 1 which would equal 11. The answer to put below the ones column then would be 5 because 11 - 6 = 5. The next row to attack is the tens column. The numbers you have to work with are 2 - 9. But remember, you already borrowed 1 value from the tens column so you would then subtract 2 - 1 which leaves you with 1 in the upper tens column minus 9 in the lower tens column. As in the previous column 1 - 9 would result in a negative number and we can't have that, so you need to borrow from the hundreds column. As you cannot subtract 1 - 9, you can subtract 11 - 9 by borrowing the value of 1 from the next column [10 + 1 = 11]. 11 - 9 = 2. Now to the hundred column. The numbers you have are 5 - 8. Remember, you have just borrowed a value of 1 from the number 5 which is 5 - 1 = 4. So the number you have on the top of the hundreds column is 4. Just like the other columns, you cannot subtract these numbers without coming up negative, so you must borrow from the column to the left. 4 - 8 will result in a negative number, so you must borrow 1 from the thousand column. 14 - 8 results in a number you can post. 14 - 8 = 6. In the last column, the thousandth place, is just the number 9. As you just borrowed one from the 9 [9-1] this number is now worth 8. Since there is no number below in the thousandth column, it is 0. So you must subtract zero from 8 to get the answer. 8 - 0 = 8. The answer to the problem 9,521 - 896 is 8,625.
Here are some resources to help you get started: Books
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