Can anyone help me solve this math problem? (Fractions)?

Question

Adding fractions with different denominators.

I haven't had math in a long time so I'm just trying to refresh my memory for school. An example will really help me. Can any one please help with this problem? Explain if you can...

Thanks a lot :)

5/8 + 11/12 + 7/15

Answer 1

First, you must find the Lowest Common Multiple (LCM) of 8,12 and 15, which is 120, since 120 = 8*15 = 12*10 = 15*8

Then you multiply 5/8 by 15 on both top and bottom to get 75/120.

Similarly you get 110/120 and 56/120 for the other 2.

Lastly, just add them up to get 241/120 or 2 1/120.

Answer 2

You're very welcome. Here we go.

5/8 + 11/12 + 7/15

As you may or may not remember, first of all you have to find the common multiple. Let's separate the denominators in factors.

8 = 2 * 2 *2 or 2^3

12= 3 * 2 * 2 = 3 * 2^2

15 = 3 * 5

Now you have to take the biggest, different factors: 3, 5, and between 2^2 and 2^3 you take 2^3 being the biggest one.

So your common multiple is 3*5*8= 120

Now to the fraction. You divide your common multiple by each denominator and then multiply that cocient times each numerator

5/8 + 11/12 + 7/15 = (75 + 110 + 84) / 120 = 269/120

And that's it. Hope it helps

Answer 3

hi

     5/(2*2*2)  + 11/(2*2*3) + 7/(3*5) ==>

=  TAKE  (2*2*2*3*5) ==>

=  5*3*5/120 + 11*10/120 + 7*8/120 =

75/120 + 110/120 + 56/120 =

(75+110+56)/120= 241/120

Answer 4

find the lowest common denominator which is 120

so 5/8 becomes 75/120

11/12 becomes 110/120

7/15 becomes 56/120

add the numerators and you get 241

answer is 241/120

Answer 5

5/8 + 11/12 + 7/15

= 1/4(5/2 + 11/3) + 7/15

(By taking 1/4 common from 1st 2 numbers)

= 1/4[(5*3 + 11*2) / (2*3)] + 7/15

(By taking LCM)

= 1/4[(15 + 22) / 6) + 7/15

=  1/4[37/6] + 7/15

= 37/24 + 7/15

(By multipling 1/4*37/6 = 37/24)

= (37*15 + 7*24) / (24*15)

= (555 + 168) / (360)

= 723 / 360

= 241/ 120

(By dividing numerator and denominator by 3)

Answer 6

5/8+11/12+7/15

120 is the lcd

75/120+110/120+56/120= 241/120= 2 1/120

Answer 7

the first two answers have the correct answer.  i think your question relates to how to find a common denominator of any group of fractions

Consider each denominator one at a time and write it in prime factored form

8 = 2x2x2   or three factors of 2

12 = 2x2x3  or two factors of 2 and one factor of 3

15 = 3x5     or one factor or 3 and one factor of 5

The common denominator (the least common multiple refered to in one answer   will have each factor the MAXIMUM  number of time that it occurs    so you have 3 factors of 2  one factor of 3 and one factor of 5

the common denominator is 2x2x2x3x5  or 120  

the follow the example in answer #2

review your prime numbers you will need to know them.  Print out a list up to about 50.  

Answer 8

Find the least common denominator (LCD):

Multiples of 8 are:

8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 104,112, 120, ...

Multiples of 12 are:

12, 24, 36, 48, 60, 72, 84, 96, 108, 120, ...

Multiples of 15 are:

15, 30, 45, 60, 75, 90, 105, 120, ...

120 seems to be the LCD,

5/8 = 75/120

11/12 = 110/120

7/15 =  56/120

75/120 + 110/120 + 56/120 = 241/120

Convert 241/120 into its lowest reduced equivalent or a mixed number:

2 1/120

Answer 9

you can't do addition or subtraction (but can do multiplication or division) with fractions with different denominators.

you have to make the denominators the same by multiplying numerator and denominator by an integer

your example has denominators of 8, 12 & 15

you can ALWAYS get to the same denominator by multiplying each fraction by all of the other denominators (top & bottom, remember!)

so 8*12*15 could be the common denominator BUT is usually easier to figure out what the LCD is (lowest common divisor)*

8=2*2*2, 12=3*2*2, 15=5*3 so we need 2*2*2*3*5=15*8 = 120 as denominator

in other words 8 *15 = 120 which gives you

(5*15) / (8*15) + 11/12 + (7*8) / (15 *8) = 75/120 + 56/120 + 11/12

and obviously 12*10 = 120 so  110/120 + 75/120 + 56/120 =

(110+75+56) / 120

=241/120 and since 241 is prime you can't factor it any further but you can put it in mixed form.

241/120 = 2 and 1/120

(edit *or is it LCM?  I forget!)

BTW, the reason 120 is lowest is that of the prime factors

2,2,2; 2,2,3 and 3,5 the set 2,2,2,3,5 allows you to get back to 8, 12,and 15 by choosing one or more of those terms.  removing any one of them would keep you from doing this:

one less 2 and you can't get to 8 (by multiplication of course), remove the 3 and 12 & 15 are out and take out the 5 and there's no way to get to 15 using that set.