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Factors of 21: As Taught by a Math Tutor
Methods
What are the Factors of 21?
As your math tutor, I’m here to guide you through the different types of factors of 21. Understanding factors is key to mastering multiplication, division, and prime numbers. Here’s a breakdown:
• Factors of 21: 1, 3, 7, 21
• Sum of Factors of 21: 32
• Negative Factors of 21: -1, -3, -7, -21
• Prime Factors of 21: 3, 7
• Prime Factorization of 21: 3^1 × 7^1
There are two main ways a math tutor would explain how to find the factors of 21: using factor pairs and prime factorization. Let’s explore both!
The Factor Pairs of 21
As your math tutor, I’m here to help you break down factor pairs of 21 step by step!
Factor pairs of 21 are any two numbers that, when multiplied together, equal 21. The question to ask is “what two numbers multiplied together equal 21?” Every factor can be paired with another factor, and multiplying the two will result in 21.
To find the factor pairs of 21, follow these steps:
Step 1:
Find the smallest prime number that is larger than 1, and is a factor of 21. For reference, the first prime numbers to check are 2, 3, 5, 7, 11, and 13. In this case, the smallest factor that’s a prime number larger than 1 is 3.
Step 2:
Divide 21 by the smallest prime factor, in this case, 3:
21 ÷ 3 = 7
3 and 7 will make a new factor pair.
Step 3:
Repeat Steps 1 and 2, using 7 as the new focus. Find the smallest prime factor that isn’t 1, and divide 7 by that number. In this case, 7 is the new smallest prime factor:
7 ÷ 7 = 1
Remember that this new factor pair is only for the factors of 7, not 21. So, to finish the factor pair for 21, you’d multiply 3 and 7 before pairing with 1:
3 x 7 = 21
Step 4:
Repeat this process until there are no longer any prime factors larger than one to divide by. At the end, you should have the full list of factor pairs.
Here are all the factor pairs for 21:
(1, 21), (3, 7)
So, to list all the factors of 21: 1, 3, 7, 21
The negative factors of 21 would be: -1, -3, -7, -21
Now you’ve got it! A math tutor would always encourage you to practice with different numbers to reinforce your understanding of factor pairs. Try another one!
Prime Factorization of 21
To find the prime factorization of 21, we break it down step by step until only prime factors remain. Then, we express 21 as a product of these prime factors multiplied together. Let’s go through the process and simplify it like a math tutor would!
The process of finding the prime factorization of 21 only has a few differences from the above method of finding the factors of 21. Instead of ensuring we find the right factor pairs, we continue to factor each step until we are left with only the list of smallest prime factors greater than 1.
Here are the steps for finding the prime factorization of 21:
Step 1:
Find the smallest prime number that is larger than 1, and is a factor of 21. For reference, the first prime numbers to check are 2, 3, 5, 7, 11, and 13. In this case, the smallest factor that’s a prime number larger than 1 is 3.
Step 2:
Divide 21 by the smallest prime factor, in this case, 3
21 ÷ 3 = 7
3 becomes the first number in our prime factorization.
Step 3:
Repeat Steps 1 and 2, using 7 as the new focus. Find the smallest prime factor that isn’t 1, and divide 7 by that number. The smallest prime factor you pick for 7 will then be the next prime factor. If you keep repeating this process, there will be a point where there will be no more prime factors left, which leaves you with the prime factors for prime factorization.
So, the unique prime factors of 21 are: 3, 7
Math Tutor Suggests: Find the Factors of Other Numbers
Practice your factoring skills by exploring how to factor other numbers, like the ones below:
Factors of 123 - The factors of 123 are 1, 3, 41, 123
Factors of 30 - The factors of 30 are 1, 2, 3, 5, 6, 10, 15, 30
Factors of 53 - The factors of 53 are 1, 53
Factors of 75 - The factors of 75 are 1, 3, 5, 15, 25, 75
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