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Solution - Least common multiple (LCM) by prime factorization

4,620
4,620

Step-by-step explanation

1. Find the prime factors of 1

1 is a prime factor.

2. Find the prime factors of 2

2 is a prime factor.

3. Find the prime factors of 12

Tree view of the prime factors of 12: 2, 2 and 3

The prime factors of 12 are 2, 2 and 3.

4. Find the prime factors of 30

Tree view of the prime factors of 30: 2, 3 and 5

The prime factors of 30 are 2, 3 and 5.

5. Find the prime factors of 84

Tree view of the prime factors of 84: 2, 2, 3 and 7

The prime factors of 84 are 2, 2, 3 and 7.

6. Find the prime factors of 165

Tree view of the prime factors of 165: 3, 5 and 11

The prime factors of 165 are 3, 5 and 11.

7. Build a prime factors table

Determine the maximum number of times each prime factor (1, 2, 3, 5, 7, 11) occurs in the factorization of the given numbers:

Prime factorNumber1 2 12 30 84 165 Max. occurrence
11000001
20121202
30011111
50001011
70000101
110000011

The prime factors 1, 3, 5, 7 and 11 occur one time, while 2 occurs more than once.

8. Calculate the LCM

The least common multiple is the product of all factors in the greatest number of their occurrence.

LCM = 12235711

LCM = 12235711

LCM = 4,620

The least common multiple of 1, 2, 12, 30, 84 and 165 is 4,620.

Why learn this

The least common multiple (LCM), sometimes called the lowest common multiple or least common divisor, is helpful for understanding the relationships between numbers. For example, if it takes Earth 365 days to orbit the sun and it takes Venus 225 days to orbit the sun and both are in perfect alignment at the time this scenario is given, how long will it take for Earth and Venus to align again? We can use LCM to determine that the answer would be 16,425 days.

LCM is also a very important part of many mathematical concepts that also have real-world applications. For example, we use LCMs when adding and subtracting fractions, which we use quite frequently.