## anonymous 5 years ago how do i find the LCD?

1. anonymous

Find multiples of each the denominators and see which ones they all have in common. Then choose the smallest of those to be your LCD.

2. anonymous

For example: Finding the LCD of 2/3, 5/12, and 7/15 we would list multiples of 3, 12 and 15

3. anonymous

The other method involves factorizing your denominator

4. anonymous

And is often a bit faster.

5. anonymous

so what if i have big number like, 220 and say 100....?

6. anonymous

Yeah, that's when factorizing helps. What are the factors of 220?

7. anonymous

how do you find the factors?

8. anonymous

22 * 10 = 220 (11*2)*(5*2) = 220 So the factors of 220 are 2*2*5*11

9. anonymous

oh, ok thanks!!

10. anonymous

Does that make sense as to how you break them down?

11. anonymous

yea sort of, i'm a little bit rusty when it comes to math....

12. anonymous

So now, what are the factors of 100?

13. anonymous

Pick two numbers you can multiply to get 100

14. anonymous

hold up one second

15. anonymous

ten and one??

16. anonymous

ten times one is ten.

17. anonymous

ok sorry, i ment ten times ten and 1 times 100

18. anonymous

yeah, don't bother with 1, it's not useful when factoring, because you can factor infinitely many ones from any number

19. anonymous

But $$10\times 10$$ is good. So now, what two numbers do you multiply to get 10?

20. anonymous

5x2 and 1x10 are the only ones i can think of right off the top of my head

21. anonymous

Right, those are the only ones. But again, the 1x10 is not useful. So we'll use 5x2

22. anonymous

So that means that $$100 = 10\times 10$$ $$100 = (5\times 2)\times (5\times 2)$$

23. anonymous

So the factors of 100 are?

24. anonymous

10?

25. anonymous

No. 2*2*5*5

26. anonymous

sorry, like i said, a bit rusty

27. anonymous

You take each number in your fully factored form those are your factors

28. anonymous

In this case we had 2*5*2*5 = 100, so 2, 2, 5, 5 would be our factors.

29. anonymous

oh, wow, thank you so much for your help!!!

30. anonymous

Ok, so now we take the factors of 100 and the factors of 220 and compare them: 100= 2*2 * 5*5 220= 2*2 * 5 * 11

31. anonymous

and the lowest is two, so the LCD would be 2??

32. anonymous

No, that's the LCF

33. anonymous

ok so whats the LCD then?

34. anonymous

The lowest common factor is 2, but the lowest common divisor is actually bigger than 100, or 220

35. anonymous

And we see that if we want them to have the same factors, we need a 11 times 100 and a 5 times 220

36. anonymous

What is 11 * 100?

37. anonymous

im looking for the lowest common denominator, not the divisor..

38. anonymous

100= 2*2 * 5*5 220= 2*2 * 5 * 11 Sorry I meant denominator

39. anonymous

oh ok, i was getting a bit confused fro a second,

40. anonymous

So again, both of our numbers have 2 2's, and one 5.

41. anonymous

But one has an extra 5, and the other has an 11.

42. anonymous

Do you see that?

43. anonymous

yep i do!

44. anonymous

Ok, so we have to make them the same

45. anonymous

So we need to multiply 100 times 11, and 220 by 5 and they will have the same factors and therefore be the same number. And that number is our LCD.

46. anonymous

oh ok!

47. anonymous

So what is 5 * 220, and 100 * 11?

48. anonymous

1100

49. anonymous

yep. Now lets have you try it with either another problem you have, or my earlier example

50. anonymous

ok lets see, how about, 95 and 100

51. anonymous

Ok, so first factor them like we did before, 100 is easy since we already had that one the last time.

52. anonymous

yep and its 10x10

53. anonymous

No, you can factor that further remember?

54. anonymous

10 is 5*2, so 100 is 5*2 * 5*2

55. anonymous

oh yea sorry, i am so sorry i apparently have lack of memory

56. anonymous

anyways, do go on...

57. anonymous

Ok, so factor 95

58. anonymous

ok 5x19 is one i know

59. anonymous

but i cant think of any others

60. anonymous

That's good. There are no others.

61. anonymous

oh ok

62. anonymous

So list the factors of 100, and the factors of 95 side by side and see which ones they have in common and which ones they do not.

63. anonymous

ok so, 100: 5x2 5x2 and for 95: 5x19 so the all have fives

64. anonymous

Ok, which ones do they not have in common?

65. anonymous

19 and 2

66. anonymous

Ok, specifically if we wanted to make them the same, what would we need to multiply by 100

67. anonymous

not really sure....

68. anonymous

100 has all the ones 95 has except?

69. anonymous

19

70. anonymous

Good. And 95 has all the ones 100 has except?

71. anonymous

2

72. anonymous

Close. It's actually two 2's and a 5. You have to count how many each one has.

73. anonymous

oh ok so with that how do you make them the same?

74. anonymous

Well you multiply the 100 by the ones it's missing (19) and the 95 by the ones it's missing (2*2*5)

75. anonymous

And they should be the same.

76. anonymous

and it would equal to 1900

77. anonymous

100 * 19 = 1900, what about 95*2*2*5?

78. anonymous

it equals the same, 1900

79. anonymous

80. anonymous

Ok try another one on your own.

81. anonymous

i will! thanks for all your help!!

82. anonymous

Any time =)

83. anonymous

wow i just did one on my own and i got it right, thank you for helping me understand!

84. anonymous

Very welcome! =)

85. anonymous

but i might need help on something else, if you have the time

86. anonymous

Oh, when you can, go ahead and give me a medal, that's how the site determines whether or not the question is answered.

87. anonymous

Of course, just start a new question and I'll take a look.

88. anonymous

ok, i have these problems where im supposed to change a percent that is a mixed number into a fraction (in lowest terms) and the book gives me no help on how to do it

89. anonymous

Ok, well start by turning the mixed number into a fraction.

90. anonymous

for example, 5 3/8 percent into a fraction

91. anonymous

Right, so start by turning the 5 3/8% into a improper fractional percentage

92. anonymous

Basically ignore the percent for now.

93. anonymous

ok hold up

94. anonymous

dont you multiplie the 5 by 3 then add 8, or am i getting this mixed up

95. anonymous

dont you do this: 5x3+8 then keep eight as your denominater

96. anonymous

No, for improper fractions, you need to rewrite 5 as $$\frac{x}{8}$$

97. anonymous

Then add it to the 3

98. anonymous

sorry, i dont know what that is

99. anonymous

5 and 3/8 $= 5 + \frac{3}{8}$$= \frac{5}{1} + \frac{3}{8}$ $= \frac{5}{1} * 1 + \frac{3}{8}$ $= \frac{5}{1}*\frac{8}{8} + \frac{3}{8}$ $= \frac{40}{8} + \frac{3}{8}$ $= \frac{43}{8}$

100. anonymous

ok, i kind of get it but kind of dont, if that makes any sense

101. anonymous

like where did the one and the eight come from>

102. anonymous

Well, you can always multiply 1 times something and get the same thing right?

103. anonymous

right...

104. anonymous

$\frac{5}{1} = \frac{5}{1}*1$

105. anonymous

oh ok....

106. anonymous

And any number over itself is 1 right?

107. anonymous

right

108. anonymous

$\frac{8}{8} = 1 \implies \frac{5}{1}= \frac{5}{1}*1 = \frac{5}{1}*\frac{8}{8} = \frac{40}{8}$ This is just a very long way to say that $5 = \frac{40}{8}$

109. anonymous

ok now it makes sense.... so ow that we have the 40/8 what do we do with it?

110. anonymous

You could also answer that by just taking the denominator and multiplying it by the whole number part.

111. anonymous

So then we add it to the fractional part.

112. anonymous

So 5 and 3/8 as a fraction is 40/8 + 3/8

113. anonymous

Take the denominator. Multiply it by the whole number. Then add that to the numerator of the fractional part. That's your improper fraction.

114. anonymous

43/8...?

115. anonymous

Yep. So 43/8 %

116. anonymous

But we want that as just a fraction, not a percent.

117. anonymous

right...

118. anonymous

So to turn a percent into fraction a we just multiply the denominator by 100.

119. anonymous

yep and that would be 800?? because you multiply 8 x 100= 800

120. anonymous

Yep.

121. anonymous

So 5 and 3/8 % = 43/800

122. anonymous

oh ok..

123. anonymous

So now you try one.

124. anonymous

ok, and i will let you know if i get it right

125. anonymous

ok

126. anonymous

ok, heres my problem: 8 4/5 change it into a percent: i got 44/5 then multiplied it by 100 and got 44/100... is that correct?

127. anonymous

No. 5 * 100 = 500, not 100.

128. anonymous

thats what i ment sorry

129. anonymous

Then yes, 44/500 is correct.

130. anonymous

yay! thanks! and im sure i will have more questions, so when i do, ill just ask!

131. anonymous

ok

132. anonymous

how do i give you a medal?

133. anonymous

ok, i have another question.....

134. anonymous

nevermind!

135. anonymous

Sorry, I had class. To give a medal you click the give medal button. next to any of my posts..