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Solution - Least common multiple (LCM) by prime factorization

13,860
13,860

Step-by-step explanation

1. Find the prime factors of 20

Tree view of the prime factors of 20: 2, 2 and 5

The prime factors of 20 are 2, 2 and 5.

2. Find the prime factors of 36

Tree view of the prime factors of 36: 2, 2, 3 and 3

The prime factors of 36 are 2, 2, 3 and 3.

3. Find the prime factors of 63

Tree view of the prime factors of 63: 3, 3 and 7

The prime factors of 63 are 3, 3 and 7.

4. Find the prime factors of 77

Tree view of the prime factors of 77: 7 and 11

The prime factors of 77 are 7 and 11.

5. Build a prime factors table

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

Prime factorNumber20 36 63 77 Max. occurrence
222002
302202
510001
700111
1100011

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

6. Calculate the LCM

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

LCM = 22335711

LCM = 22325711

LCM = 13,860

The least common multiple of 20, 36, 63 and 77 is 13,860.

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.