Carrying over or "borrowing" in subtraction may be initially confusing, but is necessary when one must subtract a bigger number from a smaller one in a larger number (for example, in 65 minus 29, 9 must be subtracted from 5). Carrying over may be difficult to grasp at first, but it is simple to do once learnt and will be convenient for everyday subtraction, whether it be that you wish to calculate gas mileage, figure out how much money you have and how much you've spent, or figure out how far you have to travel to reach a destination.
- Skill level:
- Moderately Easy
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Understand the basics of subtraction. Learning how to carry over in subtraction must come from a basic understanding of the rules of subtraction and a comprehension of why subtraction works the way it does, or the concept will soon be forgotten. The main rule in subtraction is always to subtract from top to bottom; the order of the numbers cannot be switched around. It is important for children to understand that while in addition the order of the numbers does not matter, in subtraction the bottom number must be subtracted from the top.
Recognise that the bottom number in the ones column is too large to be subtracted from the top number in the ones column. For example, in 65 minus 29, 9 is too large to be subtracted from 5. Once this is recognised, the first step in carrying over may begin.
Move to the top number in the 10s column (in 65 minus 29, move to the 6) and subtract 10 from it (so in 65 minus 29, the 6 becomes 5 to be 55). It helps to cross out the 6 and write a 5 instead.
Use the amount you took away from the top number in the 10s column and add it to the top number in the ones column. For example, in 65 minus 29, you take the 10 you took from the 6 and add it to the 5 to make it 15. It helps to add the 1 to the 5 to make it clear that it is no longer 5 you are subtracting 9 from, but 15.
Subtract the bottom number in the ones column from the new top number in the ones column. In this particular example, 15 minus 9 equals 6. Now you are free to move to the top number in the10s column (which is now 5 instead of 6) and subtract the bottom number in the tens column from it (5 minus 2 equals 3). This will give you your answer: 65 minus 29 equals 36.
If the numbers you are working with are larger than two digits, continue the same carrying over process with all the digits, moving to the left and continuing to borrow numbers.
Tips and warnings
- Keep a calculator on hand to double-check your answers when you are beginning the process of learning how to carry over in subtraction.
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