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Solution - Least common multiple (LCM) by prime factorization

225
225

Step-by-step explanation

1. Find the prime factors of 15

Tree view of the prime factors of 15: 3 and 5

The prime factors of 15 are 3 and 5.

2. Find the prime factors of 25

Tree view of the prime factors of 25: 5 and 5

The prime factors of 25 are 5 and 5.

3. Find the prime factors of 9

Tree view of the prime factors of 9: 3 and 3

The prime factors of 9 are 3 and 3.

4. Find the prime factors of 45

Tree view of the prime factors of 45: 3, 3 and 5

The prime factors of 45 are 3, 3 and 5.

5. Build a prime factors table

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

Prime factorNumber15 25 9 45 Max. occurrence
310222
512012

The prime factors 3 and 5 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 = 3355

LCM = 3252

LCM = 225

The least common multiple of 15, 25, 9 and 45 is 225.

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.