Multiples think skip counting
if a number is a multiple of another number,
it is also divisible by that number.
15 is a multiple of 3 skip count >>> 0, 3, 6, 9, 12, 15
15 is divisible by 3 15 divided by 3 is 5
15 is divisible by 3 15 divided by 3 is 5
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least common multiple - lcm
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check out the video!
the 2nd way of finding the LCM is very interesting but not the way we teach it. we use the 1st way and the Ladder method which is also on my web site.
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use the lcm to rename the denominator
when working with unlike fractions.
Adding halves and fourths does not work because they are not the same unit.
That's like trying to add apples and oranges--impossible!
We would have to rename them as fruit:
1 apple plus 1 orange = 2 fruits
That's like trying to add apples and oranges--impossible!
We would have to rename them as fruit:
1 apple plus 1 orange = 2 fruits
use the lcm to rename a new common denominator
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5 -- 2 we can't work with unlike fractions
12 9 use LCM of 36 as new denominator >>>>>>> 5 x 3 = 15 12 x what makes 36? 3 12 3 36 whatever u do to the bottom , u do to the top multiply both by 3 2 x 4 = 8_ 9 x what makes 36? 4 9 4 36 whatever u do to the bottom, u do to the top multiply both by 4 15 -- 8 = 7 subtract the numerators 36 36 36 of the renamed fractions |