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The Wonder Number Lessons

  1. Basic Counting
  2. Comparison
  3. Addition – Single Digit
  4. Addition – Double Digit
  5. Subtraction – Single Digit
  6. Subtraction – Double Digit
  7. Patterning
  8. Multiples and Factors
  9. Multiplication
  10. Primes and Composites
  11. Squares
  12. Division – No Remainder
  13. Division – With Remainder
  14. Simplifying Fractions
  15. Least Common Denominator
  16. Goldbach’s Conjecture

Lesson No. 15: Least Common Denominator

Finding the least common denominator (LCD) is an essential first step in adding fractions with unlike denominators.  Finding the least common denominator for two fractions on the Wonder Number Board is simple because all of the factoring information for each number is included in each individual block.

In the following exmaples the chip represents the numerator and the number you place it on is the denominator.

The first two fractions that we will find the least common denominator for are 1/2 and 1/3.  To begin place one blue chip on 2 to represent 1/2, and one red chip on 3 to represent 1/3.  The first number on the board that has both 2 and 3 as a factor will be the least common denominator.  Searching with a viewer you will find that the first number that meets the criteria is 6, which is a product of the factors 2 and 3 (see fig 78).  6 is the least common denominator of 2 and 3.

The next two fractions that we will find the least common denominator for are 1/4 and 1/5.  To begin place one yellow chip on 4 to represent 1/4, and one green chip on 5 to represent 1/5.  The first number on the board that has both 4 and 5 as a factor will be the least common denominator.  Searching with a viewer you will find that the first number that meets the criteria is 20, which is a multiple of the factors 4 and 5 (see fig 79).  20 is the least common denominator of 4 and 5.

The next two fractions that we will find the least common denominator for are 1/4 and 1/6.  To begin place one yellow chip on 4 to represent 1/4, and one red chip on 6 to represent 1/6.  The first number on the board that has both 4 and 6 as a factor will be the least common denominator.  Searching with a viewer you will find the first number that meets the criteria is 12, which is a multiple of both 4 and 6 (see fig 80).  12 is the lowest common denominator of 4 and 6.

© 2007 The Wonder Number Learning System, Patent No. 3975051 Dated 1976