Middle School Instruction
Some K–1 math standards such as the latest revision of the NCTM math standards and reform mathematics textbooks created since the 1990s de-emphasize or omit coverage of the LCD entirely in favor of finding any common, but not necessarily the lowest common denominator, or by using less powerful methods such as fraction strips or "benchmark" fractions. The "cross-multiply" method of comparing fractions effectively creates a common denominator by multiplying both denominators together.
Algorithm finds lowest common denominator.
Lowest common denominator for 2/9 + 1/4 + 1/6:
Start with the 3 denominators in an upside-down division box. The algorithm uses similar division boxes going downward.
Start with 2 and see if it divides exactly into any of the three denominators. Then go to 3, then 5, then 7, and so on through prime numbers.
|_9_4_6_ 2|_9_4_6_ 2 doesn't go into 9 exactly. 2 goes into 4, leaving 2, and into 6, leaving 3. 2|_9_2_3_ 2 goes into 2, leaving 1. 3|_9_1_3_ 3 is the next divisor. 3 goes into 9, leaving 3, and into 3, leaving 1. 3|_3_1_1_ 3 goes into 3, leaving 1. |_1_1_1_The process is to keep dividing the denominators until they reduce to 1. Then ignore the 1's and use the column of divisors as factors which produce the L.C.D.
2 x 2 x 3 x 3 = 36 = L.C.D.Read more about this topic: Lowest Common Denominator
Famous quotes containing the words middle, school and/or instruction:
“The middle years are ones in which children increasingly face conflicts on their own,... One of the truths to be faced by parents during this period is that they cannot do the work of living and relating for their children. They can be sounding boards and they can probe with the children the consequences of alternative actions.”
—Dorothy H. Cohen (20th century)
“A monarch, when good, is entitled to the consideration which we accord to a pirate who keeps Sunday School between crimes; when bad, he is entitled to none at all.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
“Teaching is the perpetual end and office of all things. Teaching, instruction is the main design that shines through the sky and earth.”
—Ralph Waldo Emerson (1803–1882)