What is the fraction twelve twentieths in it's simplest form

We start with 12/20. Half both numbers = 6/10. Half again = 3/5.
Because 3/5 are both odd numbers and can't be made smaller without using decimals (which you don't want to use within a fraction), 3/5 is the simplest form for this fraction.

12/20 can be simplified by factoring out the ones exg
4/8=1/2 because 4/8=1/2 times 4/4 and 4/4=1

so find factors of 12 and 20
12=2 times 2 times 3
20=2 times 2 times 5
there is 2 times 2 that is common to both so
(note: 2*2 means 2 itmes 2)
12/20=(2*2)/(2*2) times 3/5=1 times 3/5=3/5
the simplest form is 3/5