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Five-sevenths plus three twenty-firsts equals what?
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These fractions have different denominators.
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Before we can add them, we need to find a common denominator.
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Seven multiplied by three is 21.
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21 is a multiple of seven.
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So we could make both fractions into twenty-firsts.
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To get from seven to 21, we had to multiply by three.
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Three times seven is 21.
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So we need to do the same to the numerator.
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We need to multiply five by three.
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Five-sevenths is equal to fifteen twenty-firsts.
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Now we can add fifteen twenty-firsts and three twenty-firsts, which gives us a total of eighteen twenty-firsts.
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We need to simplify this fraction.
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Which number could we divide 18 and 21 by?
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Both these numbers are multiples of three.
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18 divided by three is six, and 21 divided by three is seven.
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Five-sevenths plus three twenty-firsts equals six-sevenths.
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We chose to add the fractions as twenty-firsts.
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We could also change these fractions into sevenths and add the sevenths.
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So the first thing we need to do is work out how many sevenths three twenty-firsts is.
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To get from 21 to seven, we need to divide by three.
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So we have to do the same to the numerator.
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Three divided by three is one.
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Now we can add five-sevenths and one-seventh, which makes six-sevenths.
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Both methods give us the same answer of six-sevenths.