Adding Four 3-Digit NumbersDate: 08/13/98 at 21:18:45 From: melisha Subject: Addition How do I add problems with 4 sets of numbers? For example: 457 + 458 + 954 + 958 = Date: 08/14/98 at 00:04:52 From: Doctor Mike Subject: Re: Addition Hi Melisha, I suppose you want to do it yourself and not depend on a calculator. That's great. When I do this by hand, I start off by lining them up vertically like this: 457 458 954 + 958 ----- That way I see all the numbers in the "ones" column together. Do you know what I mean by that? The far right digits in each number stand for so many ones. That's the 7, 8, 4, and another 8. The next column over has a 5 in that column for each of the 3 numbers. That 5 means 5 "tens" or 50, so that's called the "tens" column. The far left column is where the numbers stand for so many hundreds, like "4" hundreds or "9" hundreds. So, let's go. The first thing I do is to add up all the numbers in the ones column: 7 + 8 + 4 + 8 = 27. Now 27 is 20 + 7, or 2 tens and 7 ones, so I write the 7 in the ones place in the answer, and as just a reminder, I write the 2 on top in the tens column for the next step: 2 457 458 954 + 958 ----- 7 Next I add all the stuff in the tens column: 2 + 5 + 5 + 5 + 5 = 22. Keep in mind that what I am doing here is adding tens - so I have 22 tens. That is 20 tens plus 2 tens. The 20 tens is 2 hundred. (In money terms, that is like saying that 20 dimes is 2 dollars.) What I do with this is write the 2 tens as a 2 in the tens place of the answer. And as just a reminder again I write the 2 hundreds on top in the hundreds column for the next step: 2 457 458 954 + 958 ----- 27 We are almost done. I add all the hundreds 2 + 4 + 4 + 9 + 9 = 28 which means 28 hundreds, or 2 thousands and 8 hundreds. This I write down like this: 457 458 954 + 958 ----- 2827 That is the answer. The method depends on knowing about the "place value" system we use to write down numbers. That is, 1234 means 1 thousand, 2 hundred, thirty (3 tens) and 4 ones. Which "place" the digits are in says what they mean. The thing I did of writing a number temporarily on top, so I would remember, is sometimes called "carrying." It's like carrying a number fron one place to another. You carry 20 ones to the tens column where it is 2 tens. You carry 20 tens to the hundreds column where it is 2 hundreds. So that's what really happens when we add. Pretty fantastic! I hope this was what you needed to know. Please write back if you need to know something else. - Doctor Mike, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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