I am horrible in fractions

• Oct 22nd 2006, 05:05 PM
Retiredyoung24@yahoo.com
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
• Oct 22nd 2006, 05:11 PM
Jameson
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?
• Oct 22nd 2006, 05:14 PM
topsquark
Quote:

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? :) )
• Oct 22nd 2006, 05:16 PM
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
• Oct 22nd 2006, 05:19 PM
ThePerfectHacker
Quote:

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,
$\frac{3}{7}\times \frac{10}{10}=\frac{30}{70}$
$\frac{63}{70}+\frac{30}{70}=\frac{93}{70}$

Quote:

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,
$x=-49$.

Quote:

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,
$6\frac{34}{37}$
• Oct 22nd 2006, 05:24 PM
topsquark
Quote:

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
• Oct 22nd 2006, 05:27 PM
Retiredyoung24@yahoo.com
I'm even more lost now but i really appreciate the help..
• Oct 22nd 2006, 05:28 PM
topsquark
Quote:

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
• Oct 22nd 2006, 05:31 PM
Jameson
Quote:

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?!? :eek:
• Oct 22nd 2006, 05:37 PM
Retiredyoung24@yahoo.com
Quote:

Originally Posted by Jameson
What do you mean the LCD method doesn't work?!? :eek:

How does the lcd method work for number 6 if I'm combining like terms?
• Oct 22nd 2006, 05:43 PM
Jameson
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. :cool:

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)...

$\frac{45}{12}y=\frac{15}{4}y=3\frac{3}{4}*y$
• Oct 23rd 2006, 04:36 AM
dan
Quote:

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
• Dec 9th 2006, 11:10 AM
jakemaths
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