You will know because all of the numbers are prime.
The longest factor string for 840 is its prime factorization because prime factors can't be broken down any further.
Find one factor, divide by it to get the other factor. Continue separating each of the factors into smaller factors, until you only have prime numbers. For example, 840 = 2 x 420. Now continue finding smaller factors for 420.
2x2x2x3x5x7.
The GCF is 120.
Prime factor the three numbers and use each prime number the number of times it was used the most in any of the numbers. 3=3 5=5 56=2x2x2x7 2x2x2x3x5x7=840
All numbers have factors. Some factors are prime numbers. A prime factor is a factor that is a prime number. A common prime factor is a prime factor that appears on the list of factors of two or more given numbers.
840 = 23 x 3 x 5 x 7
All prime numbers have a common factor of 1.
Prime numbers have one distinct prime factor.
Prime numbers.
Since prime numbers only have one prime factor (themselves), factor trees are unnecessary.