- #1

endangered

- 4

- 0

how do i find lcm of two fractions ..say..

2/3 and 5/8

??

pls help

Thank you

2/3 and 5/8

??

pls help

Thank you

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- Thread starter endangered
- Start date

- #1

endangered

- 4

- 0

how do i find lcm of two fractions ..say..

2/3 and 5/8

??

pls help

Thank you

2/3 and 5/8

??

pls help

Thank you

- #2

tiny-tim

Science Advisor

Homework Helper

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how do i find lcm of two fractions ..say..

2/3 and 5/8

??

pls help

Thank you

Hi endangered!

The lcm of 3 and 8 is 2³.3, = 24.

(So if you want 2/3 + 5/8, you write them as 16/24 + 15/24, = 31/24.)

Note that

Generally, the lowest common multiple is found by splitting the two numbers nto their prime factors, and taking the larger power of each.

So for example, what is the lcm of 24 and 90?

Well, 24 = 2³.3, and 90 = 2.3².5, so the lcm is 2³.3².5, = 360.

- #3

endangered

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are you sure?

cause this is a assignment from my math sir..to find lcm of--repeat--FRACTIONS..

cause this is a assignment from my math sir..to find lcm of--repeat--FRACTIONS..

- #4

matt grime

Science Advisor

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We can guess, but it's better if we don't have to.

- #5

HallsofIvy

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- #6

endangered

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but this online lcm calculator returns the value of lcm of 2.3 and 3.5 as "8.0499"..

what do you have to say about that?how is it returning this definite value,if lcm of fractions does not exist?

- #7

tiny-tim

Science Advisor

Homework Helper

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but this online lcm calculator returns the value of lcm of 2.3 and 3.5 as "8.0499"..

what do you have to say about that?how is it returning this definite value,if lcm of fractions does not exist?

Because 2.3 times 3.5

Any multiple of 8.05 is also a multiple of both 2.3 and 3.5 !

Any multiple of

- #8

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- #9

uart

Science Advisor

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First off it must be clear that simply changing all references in the definition from integers to fractions will NOT make any sense. That is, if you try the definition: "the LCM of two fractions is the smallest positive fraction that is a fractional multiple of both original fractions" then it's easy to show that this is meaningless (as no such fraction exists).

The following definition does at least make sense (and I'd assume it to be the most logical way to define the LCM of fractions if we must do so). Proposed definition: "The LCM of two fractions is the smallest positive fraction that is an integer multiple of both original fractions".

Personally I've never seen the term LCM applied to fractions like this, but the above definition does seem a reasonable one. Scratching around just now with that particular definition I came up with the following interesting result:

If f1 = num1/den1 and f2 = num2/den2 are both fractions in their simplest form, then LCM(f1,f2) = LCM(num1.num2)/GCD(den1,den2).

BTW. Can anyone confirm the above result?

- #10

cheesemeister

- 1

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I need to find LCM of a list of fractions.

They're actually decimals, horrible decimals so it's much easier to display as fractions.

please note this is not an instructor/teacher set problem but a real world problem I need solving.

I have 9 incremental series, each starting at 0 and increasing by a different figure.

I need to find the smallest figure that appears in each list.

the increments are

0.04

0.05

0.0625

0.071428571

0.083333333

0.091666667

0.111111111

0.133333333

0.15

listed as fractions

1/25

1/20

1/16

1/14

1/12

11/120

1/9

2/15

3/20

any suggestions?

cheers muchly

- #11

Mark44

Mentor

- 36,656

- 8,655

Here is a list of the denominators and their factors. (Note that there are only eight, since one denominator appears twice.)

25 = 5*5

20 = 2*2*5

16 = 2*2*2*2

14 = 2*7

12 = 2*2*3

120 = 2*2*2*3*5

9 = 3*3

15 = 3*5

The LCM of these numbers will need to have as many 2's as appear the most times above, as many 3's as appear the most times above, as many 5's as appear the most times above, and as many 7's as appear the most times above.

This means there will need to be

-four factors of 2 (because 16 contains this many factors of 2)

-two factors of 3 (because 9 contains this many factors of 3)

-two factors of 5 (because 25 contains this many factors of 5)

-one factor of 7 (because 14 contains this many factors of 7)

So the LCM is 2*2*2*2*3*3*5*5*7 = 25,200

- #12

masiha

- 1

- 0

the correct ans is

lcm of the numerators divded by the hcf of the denominators:!)

lcm of the numerators divded by the hcf of the denominators:!)

- #13

- #14

Mark44

Mentor

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- #15

sqdancefan

- 2

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how do i find lcm of two fractions ..say..

2/3 and 5/8

Write the fractions using a common denominator, then find the LCM of the numerators. Divide that by the common denominator and reduce the result.

2/3 = 16/24

5/8 = 15/24

LCM(16, 15) = 16*15 = 240

LCM of 2/3, 5/8 is 240/24 = 10

____

10 = 15*2/3 = 16*5/8

- #16

sqdancefan

- 2

- 0

I need to find LCM of a list of fractions.

...

1/25

1/20

1/16

1/14

1/12

11/120

1/9

2/15

3/20

any suggestions?

cheers muchly

Your list of fractions can be expressed over the common denominator 25,200. When they are, the LCM of their numerators is 1,663,200. The ratio of these numbers is the LCM of your fractions. It is 66.

Last edited:

- #17

Diffy

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I also think that the consensus is that fractions do not have LCMs.

Perhaps we should lock this so it doesn't creep up to the front page next year.

- #18

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I also think that the consensus is that fractions do not have LCMs.

Perhaps we should lock this so it doesn't creep up to the front page next year.

Agreed!

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