Wednesday, June 24, 2009

Practice problems for prime factorization

Find the prime factorizations of the following numbers.

a) 128
b) 129
c) 130

d) Find all the factors of 130.

Answers in the comments.
at

2 comments:

  1. Prof. HubbardJune 24, 2009 at 8:30 PM

    a) 128 = 2*64 2 is prime, 64 is not
    64 = 8*8 not primes
    8 = 2*4 2 is prime, 4 is not
    4 = 2*2

    128=2*8*8 becomes
    128 = 2*2*2*2*2*2*2 = 2^7

    b) 129 = 3*43 3 is prime and 43 is prime so we are done.
    129 = 3*43

    c) 130 = 13*10, 13 is prime and 10 is not
    10 = 2*5 both are prime
    130 = 2*5*13

    ReplyDelete
  2. Prof. HubbardFebruary 10, 2011 at 7:49 PM

    For part d), let's use the fact we already know that 130 = 2 * 5 * 13. We always start the factor list with 1 and the original number.

    1 and 130
    2 and 65
    (not 3)
    (not 4)
    5 and 26
    (not 6, 7, 8 or 9)
    10 and 13

    So the whole list from lowest to highest is:
    1, 2, 5, 10, 13, 26, 65 and 130.

    ReplyDelete

If you have general questions, you can leave them here and Professor Hubbard will answer them.

Note: Only a member of this blog may post a comment.