# Thread: I am horrible in fractions

1. ## 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

2. I'll do one and see if you can follow the method.

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

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

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

Do you see the method?

3. Originally Posted by Retiredyoung24@yahoo.com
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.

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

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

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

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

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

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

-Dan

(Jameson, why is it we always pick the same examples to do? )

4. I got the same answer but wasn't sure if I was right, but the lcd method doesn't work for the following problems

5. Originally Posted by Retiredyoung24@yahoo.com
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
$\frac{9}{10}\times \frac{7}{7}=\frac{63}{70}$
And,
$\frac{3}{7}\times \frac{10}{10}=\frac{30}{70}$
$\frac{63}{70}+\frac{30}{70}=\frac{93}{70}$

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

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:
$4\frac{5}{8}=\frac{4\times 8+5}{8}=\frac{37}{8}$
Thus,
$32\div \frac{37}{8}=\frac{32}{1}\times \frac{8}{37}$
Thus,
$\frac{256}{37}$
Express back as mixed number,
$6\frac{34}{37}$

6. Originally Posted by Retiredyoung24@yahoo.com
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: $x = 6 \, \frac{2}{3} = 6 \cdot \frac{3}{3} + \frac{2}{3} = \frac{18}{3} + \frac{2}{3} = \frac{18+2}{3} = \frac{20}{3}$

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

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

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

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

-Dan

7. I'm even more lost now but i really appreciate the help..

8. Originally Posted by Retiredyoung24@yahoo.com
I'm even more lost now but i really appreciate the help..
Where specifically are you getting lost?

-Dan

9. Originally Posted by Retiredyoung24@yahoo.com
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?!?

10. Originally Posted by Jameson
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?

11. 6. 6 5/6y - 3 1/12 y Combine like terms

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

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

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

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

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

$\frac{45}{12}y=\frac{15}{4}y=3\frac{3}{4}*y$

12. Originally Posted by Retiredyoung24@yahoo.com
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 $x$ is the same as mulypling by $\frac{1}{x}$

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

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

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

which is b.

Dan

13. ## 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