Please please please help me do these problems im stuck =/ math homework help?

Question

Find the LCM of 3, 9, and 20.

Find the LCM of 50 and 70.

Find the LCM of 21 and 28.

Find the LCM of 25 and 10

Find the LCM of 3, 5, and 7.

Answer 1

The brute force method is to completely factor each number, then Union the results....

3 = 3

9 = 3*3

20 = 2*2*5

So you need 2 twos, 2 threes and a 5 or

2*2*3*3*5

or

180

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50 = 2*5*5

70 = 2*5*7

So, 1 two, 2 fives and 1 seven

2*5*5*7 = 350

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The others can be found in the same way....

Answer 2

This page explains how to find the LCM:

http://mathforum.org/library/drmath/view...

Answer 3

How? It's easy.

3 = 3, 9 = 3(3), 20 = 2(2)(5) LCM = 3(3)(2)(2)(5) = 180

50 = 2(5)(5), 70 = 2(5)(7) LCM = 2(5)(5)(7) = 350

21 = 3(7), 28 = 2(2)(7) LCM = 2(2)(3)(7) = 84

25 = 5(5), 10 = 2(5) LCM = 2(5)(5) = 50

3 = 3, 5 = 5, 7 = 7 LCM = 3(5)(7) = 105