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Thread: I am horrible in fractions

  1. #1
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    I am horrible in fractions

    I have 8 problems that I need to submit for homework they are multiple choice


    1. 9/10 + 3/7

    a. 12/17
    b. 2/7
    c. 93/70
    d. 1


    2. 18 = 4 - 2/7x

    a. 77
    b. -4
    c. -49
    d. -6 2/7


    3. Evaluate: 4 - 1/2xy, for x = 6 2/3 and y = -5/6

    a. 6 7/9
    b. 5
    c. -2/3
    d. 1 1/3


    4. 7 5/6 + 2 3/4 Add.

    a. 9 7/12
    b. 9 4/5
    c. 10 7/12
    d. 9 2/3

    5. 2 1/4 - 9 4/7 Subtract.

    a. -8 9/28
    b. -7 9/28
    c. 8 9/28
    d. 7 9/28


    6. 6 5/6y - 3 1/12 y Combine like terms

    a. 3 3/4y
    b. 3 1/3y
    c. -3 2/3y
    d. 3 3/4


    7. (-5 3/4) . (- 3 7/9) Multiply

    a. 21 13/18
    b. 15 7/12
    c. 8 3/4
    d. -9 19/36


    8. 32 divided by 4 5/8

    a. 8 1/40
    b. 6 34/37
    c. 148
    d. 8 5/8
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  2. #2
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    I'll do one and see if you can follow the method.

    $\displaystyle \frac{9}{10}+\frac{3}{7}$

    You can either find the LCD (lowest common denominator) or just find any common denominator and then reduce. The LCD of 10 and 7 is 70... SO

    $\displaystyle \frac{63}{70}+\frac{30}{70}=\frac{93}{70}$

    Do you see the method?
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    I have 8 problems that I need to submit for homework they are multiple choice


    1. 9/10 + 3/7

    a. 12/17
    b. 2/7
    c. 93/70
    d. 1
    Like the rest, this is an exercise in denominators. I am going to rewrite the fractions with the denominator 7*10 = 70.

    $\displaystyle \frac{9}{10} = \frac{x}{70}$

    $\displaystyle x = 70 \cdot \frac{9}{10} = 63$

    And:
    $\displaystyle \frac{3}{7} = \frac{y}{70}$

    $\displaystyle y = 70 \cdot \frac{3}{7} = 30$

    So
    $\displaystyle \frac{9}{10} + \frac{3}{7} = \frac{63}{70} + \frac{30}{70}$

    Now that we've done this, we can simply add the numerators:
    $\displaystyle \frac{63}{70} + \frac{30}{70} = \frac{63+30}{70} = \frac{93}{70}$

    Which is answer c).

    -Dan

    (Jameson, why is it we always pick the same examples to do? )
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  4. #4
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    I got the same answer but wasn't sure if I was right, but the lcd method doesn't work for the following problems
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  5. #5
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    I have 8 problems that I need to submit for homework they are multiple choice


    1. 9/10 + 3/7

    a. 12/17
    b. 2/7
    c. 93/70
    d. 1
    $\displaystyle \frac{9}{10}\times \frac{7}{7}=\frac{63}{70}$
    And,
    $\displaystyle \frac{3}{7}\times \frac{10}{10}=\frac{30}{70}$
    Add them,
    $\displaystyle \frac{63}{70}+\frac{30}{70}=\frac{93}{70}$

    2. 18 = 4 - 2/7x
    Multiply by seven,
    $\displaystyle 18\cdot 7=7\cdot 4-2x$
    Thus,
    $\displaystyle 126=28-2x$
    Subtract 28 from both sides,
    $\displaystyle 98=-2x$
    Divide by -2 thus,
    $\displaystyle x=-49$.

    8. 32 divided by 4 5/8

    a. 8 1/40
    b. 6 34/37
    c. 148
    d. 8 5/8
    We need to express the mixed fraction as a improper fraction:
    $\displaystyle 4\frac{5}{8}=\frac{4\times 8+5}{8}=\frac{37}{8}$
    Thus,
    $\displaystyle 32\div \frac{37}{8}=\frac{32}{1}\times \frac{8}{37}$
    Thus,
    $\displaystyle \frac{256}{37}$
    Express back as mixed number,
    $\displaystyle 6\frac{34}{37}$
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  6. #6
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    3. Evaluate: 4 - 1/2xy, for x = 6 2/3 and y = -5/6

    a. 6 7/9
    b. 5
    c. -2/3
    d. 1 1/3
    First: $\displaystyle x = 6 \, \frac{2}{3} = 6 \cdot \frac{3}{3} + \frac{2}{3} = \frac{18}{3} + \frac{2}{3} = \frac{18+2}{3} = \frac{20}{3}$

    So.
    $\displaystyle 4 - \frac{1}{2} \cdot xy = 4 - \frac{1}{2} \cdot \frac{20}{3} \cdot \frac{-5}{6}$

    = $\displaystyle 4 + \frac{1 \cdot 20 \cdot 5}{2 \cdot 3 \cdot 6}$ (The extra negative on the 5 cancelled the subtraction, making it an addition.)

    = $\displaystyle 4 + \frac{100}{36} = 4 + \frac{25}{9} = 4 \cdot \frac{9}{9} + \frac{25}{9} = \frac{36}{9} + \frac{25}{9} = \frac{36+25}{9} = \frac{61}{9}$

    Now we need to write this as a mixed fraction:
    = $\displaystyle \frac{9 \cdot 6 + 7}{9} = \frac{9 \cdot 6}{9} + \frac{7}{9} = 6 \, \frac{7}{9}$

    So the answer is a)

    -Dan
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  7. #7
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    I'm even more lost now but i really appreciate the help..
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  8. #8
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    I'm even more lost now but i really appreciate the help..
    Where specifically are you getting lost?

    -Dan
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  9. #9
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    I got the same answer but wasn't sure if I was right, but the lcd method doesn't work for the following problems
    What do you mean the LCD method doesn't work?!?
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  10. #10
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    Quote Originally Posted by Jameson View Post
    What do you mean the LCD method doesn't work?!?
    How does the lcd method work for number 6 if I'm combining like terms?
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  11. #11
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    6. 6 5/6y - 3 1/12 y Combine like terms

    $\displaystyle 6\frac{5}{6}=\frac{6*6+5}{6}=\frac{41}{6}$

    $\displaystyle 3\frac{1}{12}=\frac{3*12+1}{12}=\frac{37}{12}$

    Now you have $\displaystyle \frac{41}{6}y-\frac{37}{12}y$

    You can't subtract these directly because they don't have... a common denominator! Yes this stuff never goes away.

    Anyway, let's get the LCD.

    LCD(6,12)=12

    So $\displaystyle \frac{82}{12}y-\frac{37}{12}y=\frac{45}{12}y$

    Now convert back to mixed number (which I think is stupid)...

    $\displaystyle \frac{45}{12}y=\frac{15}{4}y=3\frac{3}{4}*y$
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  12. #12
    dan
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    Quote Originally Posted by Retiredyoung24@yahoo.com View Post
    I have 8 problems that I need to submit for homework they are multiple choice

    8. 32 divided by 4 5/8

    a. 8 1/40
    b. 6 34/37
    c. 148
    d. 8 5/8
    dividing by $\displaystyle x$ is the same as mulypling by $\displaystyle \frac{1}{x}$

    so you have $\displaystyle 32 * \frac{1} {4 5/8} $ or
    $\displaystyle 32*\frac{1}{37/8} $
    or
    $\displaystyle \frac{32}{37/8} $

    mutiply the top and bottem by 8 to get $\displaystyle \frac{256} {37}$

    re-write as $\displaystyle 6\frac{34}{37}$

    which is b.


    Dan
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  13. #13
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    fractions

    try this method

    3+12
    7 3 = 7x3= 21 common denom
    3x3 9/21 7x12=84/21 so we have 9/21+84/21=93/21

    or a+b axd+cxb
    c d= cxd
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