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Calculate the following, 10.2079 plus 48.4128.
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The two numbers in this addition are interesting because they’re fairly long decimal numbers.
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Each number contains two digits to start with.
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They’re the tens and the ones.
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And then, there are four digits after the decimal point.
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That means we go as far as ten thousandths.
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Before we add the two numbers together, we can have a quick estimate of what we think the answer is going to be.
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We can see that the whole number part of these numbers adds up to 58.
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10 plus 48 equals 58.
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And then, it looks like the decimal part of these numbers is not going to add up to another one.
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So, it looks like our answer is going to be 58 point something.
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Let’s use the column method to find the answer and to see if our prediction is correct.
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First, we’ll write the addition out.
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And we’ll set it out vertically.
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And the best way to do this and to make sure that the digits are in the correct columns is to make sure that the decimal points are lined up.
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Once we’ve done that, we can fill in the digits around the decimal points.
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And we know that each set of digits has the correct value.
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Finally, before we start adding, let’s put another decimal point in between the equal sign.
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This way we know we definitely won’t forget it.
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As usual, we’re going to work from right to left.
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So, we’re going to begin here with the ten thousandths column nine ten thousandths plus eight ten thousandths equals 17 ten thousandths.
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On to the thousandths column, seven thousandths plus two thousandths equals nine thousandths, plus the one we’ve exchanged equals ten thousandths, which is the same as one hundredth.
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We’ve only got one hundredth in the top part of the addition, but we’ve also exchanged one, so we have two hundredths altogether.
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And two tenths plus four tenths equals six tenths.
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Notice how we didn’t have to exchange any ones there, so it looks like our prediction is going to be correct.
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The answer is going to be 58 point something.
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Zero ones plus eight ones equals eight ones.
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And one 10 plus four tens equals five tens.
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Because there wasn’t a clear mental method to find the answer, we decided to use the column method.
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We wrote the two decimals out on top of each other and then we added the columns from right to left, remembering to put the decimal point in our answer.
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10.2079 plus 48.4128 has a total of 58.6207.