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:
“In middle age, I practiced feeling old, but the real thing has been a rude surprise.”
—Mason Cooley (b. 1927)
“The future is built on brains, not prom court, as most people can tell you after attending their high school reunion. But you’d never know it by talking to kids or listening to the messages they get from the culture and even from their schools.”
—Anna Quindlen (b. 1953)
“Much of the pressure contemporary parents feel with respect to dressing children in designer clothes, teaching young children academics, and giving them instruction in sports derives directly from our need to use our children to impress others with our economic surplus. We find “good” rather than real reasons for letting our children go along with the crowd.”
—David Elkind (20th century)