Question

Help! word problem but what do I use to figure it out fractions?:
Family moving has 3 clocks in a box. 1 beeps at 8 mins, 2 beeps at 10mins and 3 beeps at 12 mins....if they all beep together at 3pm when will they next beep together again?

Answer 1

find least common multiple of your numbers

Answer 2

is see you get 5 per hour easy enough

Answer 3

Like that its multiples of 2 or even numbers?

Answer 4

8/5.....5/8

Answer 5

the LCM of the three time intervals, i.e. LCM 8, 10 and 12. They will beep together after that many minutes.

Answer 6

apoorvk, I dont understand

Answer 7

Hmm. Okay. now what does LCM mean first of all?
Suppose the LCM of 4, 6, and 8 is 24. Okay we can all find that. But, what does it signify? Any idea?

Answer 8

I guess you may have to explain as if I'm from Mars

Answer 9

pattern that repaets?

Answer 10

No probs, I 'll try to do that if required :)

Take your time and think.

Answer 11

Im not sure where to start the thinking...

Answer 12

Umm kinda but let me make it better.

Least Common Multiple is exactly what it is named as!!

It means in the tables of the 4, 6, 8 each, which is the first *common* no. that happens? 24 is.

Answer 13

So, do you know how to find the LCM?

Answer 14

the multiples will be equall in an LCM right?

Answer 15

the patteren of the 8, 10 ,12 makes the LCM: Im computing

Answer 16

keep multiplying untill the three numbers have the same answer, right?

Answer 17

8 x what equalls the same as 10 x what....right?

Answer 18

yes, they will be equal, since it is a "common" multiple. you are thinking well there!

And that is exactly what we are doing with the clocks up there. one beeps every 8 mins (that is in the multiple of 8 mins). SO it beeps at 3pm, then 3.08 pm, then 3.16 pm and so on...
The next one beeps every 10mins, so it beeps first at 3pm, next at 3.10 pm, next at 3.20 pm, and so on..
And similarly the last one beeps every 12 mins, so it beeps at 3pm, 3.12 pm, 3.24 pm, and so on...


they beep after their respective time periods. So a time will come when they are synchronised again and that 'll be after the LCM minutes of 8, 10 and 12

Answer 19

My mind wants to make a clock face and count off the hours that are common, but this seems the long way.....is there a math solution to the fraction that gets me the LCM without trying to count it on a clock face?

Answer 20

Ofcourse, there is a way to solve an LCM, because if we have really large nos. or more than 2 numbers, its very difficult compute that mentally.

Please have a look at these links (there is a text link and a video), this should help you with the method of finding LCM of any nos.
http://www.mathplayground.com/howto_gcflcm.html
http://www.math.com/school/subject1/lessons/S1U3L3DP.html

I 'll help you out, if after this you get any trouble :)

Answer 21

thank you!

Answer 22

And do post your answer, so that we can verify it for you!

Answer 23

so every 120 mins. they repeat together?

Answer 24

Yes, exactly! Correct-o!!

Were you able to learn the process of finding LCMs okay?

Answer 25

yes thank you!