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albertw

  • 3 years ago

can someone explain to me how to add 5/20 and 6/15 I don't understand lowest common denominators?

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  1. misterf
    • 3 years ago
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    A really easy way to do this (although not the most efficient) is to just start listing all the multiples of the denominators:

  2. julie
    • 3 years ago
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    Yeah, basically you can't add two fractions unless they have the same denominator.

  3. misterf
    • 3 years ago
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    the denoms are 20 and 15, so list the multiples: 15: 15, 30, 45, 60, 75 ... 20: 20, 40, 60, 80 ...

  4. misterf
    • 3 years ago
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    here you can move from left to right until you find one that's in both lists :)

  5. albertw
    • 3 years ago
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    hmmm, ok, so how would I add them?

  6. julie
    • 3 years ago
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    misterf nailed it :)

  7. julie
    • 3 years ago
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    Ok so once you find the common denominator -- above, we see that it would be 60.

  8. siddharth
    • 3 years ago
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    Well, to add or subtract fractions, you have to make sure the bottom numbers on both fractions are the same. So, the best way to add two fractions with different denominators is to find the Lowest Common Multiple, and change the fractions to that form to perform the addition.

  9. julie
    • 3 years ago
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    Then you find how you make the denominators of both the same as that common one. So 15 * 4 = 60 and 20 * 3 = 60.

  10. julie
    • 3 years ago
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    Then you multiply the numerator, too: 6 * 4 = 24 15 * 4 = 60 and 5 * 3 = 15 20 * 3 = 60

  11. misterf
    • 3 years ago
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    \[\frac{5}{20} = \frac{15}{60}\] \[\frac{6}{15} = \frac{24}{60}\] then add them normally: \[\frac{15}{60} + \frac{24}{60} = \frac{39}{60}\] does this make sense?

  12. julie
    • 3 years ago
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    Haha misterf beat me to it :)

  13. misterf
    • 3 years ago
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    please gimme a medal if i helped i am collecting them :p

  14. julie
    • 3 years ago
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    When you add two fractions and they have the same denominator, the denominator stays the same and you just add the numerators.

  15. julie
    • 3 years ago
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    Gave it! :)

  16. siddharth
    • 3 years ago
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    Misterf explained it really nicely. Let us know if you don't understand something, albertw. I gave you a medal as well, misterf :)

  17. misterf
    • 3 years ago
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    yay!!

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