Answers

2016-01-19T18:59:59+08:00
Find the LCM of the denominators. For example, we have,  \frac{5}{6} and  \frac{6}{7}

We need to find the LCM of the denominators, which are 6 and 7. To get LCM, list the prime factors of the numbers.

6 = 2 × 3
7 = 7

Then, just multiply the prime numbers, but not all (you'll understand better in the next example. ☺).

2 × 3 × 7 = 42

Therefore, the LCD/LCM in my example is 42.

Another example.  \frac{25}{30} and  \frac{35}{45}

30 = 2 × 3 × 5
45 = 3 × 3 × 5

Multiply. 30 & 45 have common prime factor, which is 3 and 5, just multiply the numbers once. (The numbers are bold)
× 3 × 3 × 5 = 90

Therefore, the LCM/LCD in my example is 90.


I hope that you'll understand it even if I haven't explained it well. ☺

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Also, if you think that the two numbers have no common factors, just multiply them. (Example no. 1)