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# What is the LCM of 40 and 66?

What is the loest common multiple of 40 and 66

Thanks x

I do take notice in class i know i have to do 2 factor trees get their prime factors of 40 and 66 work out the equation which is 2 cubed x 3x 5x 11 but just want to check i have got it right!

5 years ago

Member since:
18 November 2007
Total points:
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## Best Answer - Chosen by Voters

Here's a way to do it without the factor trees:

40 x 1 = 40
40 x 2 = 80
40 x 3 = 120
40 x 4 = 160
40 x 5 = 200
40 x 6 = 240
40 x 7 = 280
40 x 8 = 320
40 x 9 = 360
40 x 10 = 400
40 x 11 = 440
40 x 12 = 480
40 x 13 = 520
40 x 14 = 560
40 x 15 = 600
40 x 16 = 640
40 x 17 = 680
40 x 18 = 720
40 x 19 = 760
40 x 20 = 800
40 x 21 = 840
40 x 22 = 880
40 x 23 = 920
40 x 24 = 960
40 x 25 = 1000
40 x 26 = 1040
40 x 27 = 1080
40 x 28 = 1120
40 x 29 = 1160
40 x 30 = 1200
40 x 31 = 1240
40 x 32 = 1280
40 x 33 = 1320

66 x 1 = 66
66 x 2 = 132
66 x 3 = 198
66 x 4 = 264
66 x 5 = 330
66 x 6 = 396
66 x 7 = 462
66 x 8 = 528
66 x 9 = 594
66 x 10 = 660
66 x 11 = 726
66 x 12 = 792
66 x 13 = 858
66 x 14 = 924
66 x 15 = 990
66 x 16 = 1056
66 x 17 = 1122
66 x 18 = 1188
66 x 19 = 1254
66 x 20 = 1320

Therefore, 1320 is the least common multiple.
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• by anne w
Member since:
22 February 2009
Total points:
2,881 (Level 4)
I think you are confusing Lowest common multiple with Highest common factor? ( you are not alone in doing this!!)

The way I try to help my students remember is if the word "multiple" is in the question, your answer will be a larger number than the question ones.
It means that you write one of the numbers times table out for a few lines and then the other's and when you have written the same number in both times tables that is the LCM

So, for example, the LCM of 15 and 9 is 45...

15 x 1 = 15 9 x 1 = 9
15 x 2 = 30 9 x 2 = 18
15 x 3 = 45 9 x 3 = 27
15 x 4 = 60 9 x 4 = 36
15 x 5 = 75 9 x 5 =45
45 appears in both sets of times tables so it is the Lowest Common Mulitple

An easier way is always to start with the highest number and start writing out its table. As soon as you spot a number that would be in the other ones table then you have found the LCM!

(If you had been asked to find the Highest Common Factor of 15 and 9 then you would have done as you said, write the factor trees for each and see which is the lowest number they share. In this case it would be 3)

### Source(s):

I'm a maths teacher
• by Jeremy W
Member since:
20 September 2007
Total points:
1,653 (Level 3)
the lcm of two numbers is defined as being the product of the two numbers divided by their gcd, now-

gcd(40, 66) = 2,

and the product of 40 and 66 is 2640, so

lcm(40, 66) = 2640 / 2 = 1320

and that number represents the lowest possible number that 40 and 66 will both divide

### Source(s):

• 1 person rated this as good
• Member since:
10 December 2006
Total points:
392 (Level 2)
stanschi is correct.
Lowest Common Multiple is always larger than than the 2 numbers High Common Factor is always lower than the 2 numbers -or more if you are given more.
• by SS4
Member since:
02 December 2006
Total points:
57,374 (Level 7)
40 = 2*2*10
66 = 2*3*11

LCM = 2*2*10*3*11 = 1320

note this is the same answer as the guy who posted out the long multiple list and is far quicker
• by knownout
Member since:
28 March 2009
Total points:
38,460 (Level 7)
2
• by John
Member since:
24 July 2009
Total points:
3,574 (Level 4)
You should take more notice in class. Do it yourself!