to simplify this fraction you find a number that both the top and bottom can be divided by. in this case both can be divided by 3 turning the fraction to 3/5.
to make it a decimal we take the simplified 3/5 and multiply it by 2 making it 6/10. now that the bottom is 10 we take the 6 and put it in the tenths place of a decimal. so it would be 0.6. or you could divide the top by the bottom, 3 divided by 5 is also 0.6.