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Solution - Least common multiple (LCM) by prime factorization

28,560
28,560

Step-by-step explanation

1. Find the prime factors of 68

Tree view of the prime factors of 68: 2, 2 and 17

The prime factors of 68 are 2, 2 and 17.

2. Find the prime factors of 119

Tree view of the prime factors of 119: 7 and 17

The prime factors of 119 are 7 and 17.

3. Find the prime factors of 120

Tree view of the prime factors of 120: 2, 2, 2, 3 and 5

The prime factors of 120 are 2, 2, 2, 3 and 5.

4. Find the prime factors of 240

Tree view of the prime factors of 240: 2, 2, 2, 2, 3 and 5

The prime factors of 240 are 2, 2, 2, 2, 3 and 5.

5. Build a prime factors table

Determine the maximum number of times each prime factor (2, 3, 5, 7, 17) occurs in the factorization of the given numbers:

Prime factorNumber68 119 120 240 Max. occurrence
220344
300111
500111
701001
1711001

The prime factors 3, 5, 7 and 17 occur one time, while 2 occurs 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 = 222235717

LCM = 2435717

LCM = 28,560

The least common multiple of 68, 119, 120 and 240 is 28,560.

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.