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:
“Said, All you needed to do was just explain;
Reason Reason is my middle name.”
—Josephine Miles (1911–1985)
“Loosed betwixt eye and lid, the swimming beams
Of memory, blind school of cuttlefish,
Rise to the air, plunge to the cold streams....”
—Allen Tate (1899–1979)
“One year, I’d completely lost my bearings trying to follow potty training instruction from a psychiatric expert. I was stuck on step on, which stated without an atom of irony: “Before you begin, remove all stubbornness from the child.” . . . I knew it only could have been written by someone whose suit coat was still spotless at the end of the day, not someone who had any hands-on experience with an actual two-year-old.”
—Mary Kay Blakely (20th century)