Homework help for mom about fractions...?

Question

Trying to help my son with adding and subtracting fractions. I can't remember how to get the common demoninator. Example:1/8+4/6+7/10=? Can someone please explain it to me so that I can help him. Thanks

Answer 1

well u first get the biggest denominator, which is ten, and then start counting its multiples "10, 20, 30...." untill u get a number which all three denominators are divisible by..which may take some time!

or you can convert them into decimals and then add them and then re-change them into a fraction...I guess =(

Answer 2

Find the lowest common denominator.

in this case it is 120  

8 x 15 = 120

6 x 20 = 120*

10 x 12 = 120

Now convert your fractions

15 x 1 = 15 (1/8)

4 x 20 = 80  (4/6)

12 x 7 = 84 (7/10)

so 15/120 + 80/120 + 84/120

*Remember also to simplify 1st ie 4/6 is 2/3

(i didn't but would do that 1st on a math problem)

1 59/120 is the simplification so this is correct nice JOB!

Math teachers always want the simplified answer if the answer had been 180/120 then your simplified answer would have been (1st) 18/12 then 1  6/12  then further 1  1/2.

This is just to clarify simplifying

Answer 3

Hi,

It's nice of you to help your son out,

okay, heres how you do it (in a stepwise manner), I got a little to into the question and went on to solve it.

You currently have the following fractions...

1+4+7

_  _  _

8  6  10

if you multiply each of the denominators, the a common denominator can be found, (8* 6 *10 = 480)

So, for this question, the a common denominator is 480.

Now, the next step, is to change the fractions, so that they each have a denominator of 480. The trick is, number you multiply the denominator by, you have to multiply the numerator by, so you get...

1 x 60    60

--------- = ---

8 x 60     480

So you can do this to each of the other fractions to obtain...

60       320     336

----   + ------ +  -----

480     480      480

So now, you add the numerators (60 +320 +336 = 716) and divide it by the common denominator...

Thus, your answer is

716

-----

480

This can be simplified by dividing the numerator and denominator by 4 (remember, what you do to the top, you must do to the bottom)

And you get...

179

-----

120

And your done! :)

I hope this helped:)

Good Luck

(I know this working looked quite ugly, sorry)

*Edit:

Yes you can simplify that answer further, by seeing how many times 120 goes into 179, the answer is one, and the remainder is 59/120.

so you get

1    59/120

(not 1      59/100   by i assume you has a typo) :)

Answer 4

First, finding the least common denominator (LCD)

Express each number as a product of prime numbers:

8 = 2x2x2    

6 = 2x3    

10 = 2x5

As we can see, the largest number of 2's appearing in any of these products is 3. Therefore, the LCD must contain three 2's

LCD = 2x2x2x.....

Again, the largest number of 3's appearing in any product is 1. The LCD must contain one 3

LCD = 2x2x2x3x...

Again the largest number of 5's appearing in these products is 1. So the LCD must contain one 5

LCD = 2x2x2x3x5 = 120

Since there are no more prime factors in any of these products, we are done

Now

120/8 = 15,   so   1/8  =  (1x15) / (8x15)  =  15/120

120/6 = 20,   so   4/6  =  (4x20) / (6x20)  =  80/120

120/10 = 12, so  7/10  = (7x12) / (10x12) =  84/120

and

1/8 + 4/6 + 7/10 = 15/120 + 80/120 + 84/120 = (15+80+84)/120 = 179/120

P.S. A quick way to calculate a common denominator is to simply multiply all the denominators. Then you would get 8x6x10 = 480.

The answer would then have been 716/480.

You would then have simplified this fraction by dividing the numerator and denominator by 4 giving 179/120, the same answer as above.

Answer 5

The common denominator comes when all those numbers can be divided by a number without any decimal values ...........................8,6,10 can be divided by 120........................................ 3,4,8.can be divided by 24....................................so this means that the common denominator can be found by finding a number that all the numbers can be divided by without a decimal value..........................and can you please if you want select my answer as the best answer.....

Answer 6

lcd is 120

so 1/8+4/6+7/10= 15/120 + 80/120 + 84/120 =  (add numerators)

Answer 7

8 = 2 x 2 x 2

6 = 2 x 3

10 = 2 x 5

-------------------------

The LCM of 8 , 6 , 10 is:

2 x 2 x 2 x 3 x 5

= 120

1/8 + 4/6 + 7/10

= (1 x 15)/(8 x 15) + (4 x 20)/(6 x 20) + (7 x 12)/(10 x 12)

= 15/120 + 80/120 + 84/120

= (15 + 80 + 84)/120

= 179/120

= 1 (179 - 120)/120

= 1 59/120