Chapter 2: Problem 272
In the following exercises, find the prime factorization of each number using the factor tree method. $$ 420 $$
Short Answer
Expert verified
420 = 2^2 × 3 × 5 × 7
Step by step solution
01
- Start with the given number
Write the number 420 at the top of your factor tree.
02
- Find two factors of 420
Choose any two numbers that multiply to give 420. For example, 2 and 210 (since 420 = 2 × 210). Draw branches down from 420 and write 2 and 210.
03
- Factor the remaining composite number (210)
Next, take the number 210 and find two factors of it. For instance, 2 and 105 (since 210 = 2 × 105). Draw branches down from 210 and write 2 and 105.
04
- Continue factoring the composite numbers
Now, take the number 105 and find its factors. For example, 3 and 35 (since 105 = 3 × 35). Draw branches down from 105 and write 3 and 35.
05
- Factor 35 further
Finally, take the number 35 and factor it into 5 and 7 (since 35 = 5 × 7). Draw branches down from 35 and write 5 and 7.
06
- List all prime factors
Now, list out all the prime numbers at the ends of the branches: 2, 2, 3, 5, and 7.
07
- Write the prime factorization
Combine the prime factors to express 420 as a product of primes: 420 = 2^2 × 3 × 5 × 7.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Factor Tree Method
The factor tree method is a simple way to find the prime factors of a composite number. Imagine a tree where the given number is the root, and branches grow down as we break the number into smaller factors. To start:
- Write the number at the top.
- Then, find two factors of that number.
- If these factors are not prime, keep factoring them until only prime numbers remain.
Composite Numbers
Composite numbers are numbers that have more than two distinct positive divisors: 1 and the number itself, plus at least one additional divisor. In simpler terms, a composite number can be divided evenly by numbers other than 1 and itself. For example:
- 4 is composite because it can be divided by 1, 2, and 4.
- 15 is composite because it can be divided by 1, 3, 5, and 15.
Prime Numbers
Prime numbers are the opposite of composite numbers. A prime number only has two distinct positive divisors: 1 and itself. In other terms, these numbers cannot be evenly divided by any other number. Examples include:
- 2, as it can only be divided by 1 and 2.
- 3, as it can only be divided by 1 and 3.
Multiplication
Understanding multiplication is crucial for both creating and checking factor trees. Here's a quick recap:
- Multiplication is combining groups of equal sizes. For example, 4 × 3 means 4 groups of 3.
- In the factor tree method, you're essentially reversing multiplication by breaking numbers down to their smaller factors.
- To verify the prime factorization, you multiply the prime factors together to get the original number. For instance, with 420: 2^2 × 3 × 5 × 7 should equal 420.