It's easier if you look at it in terms of percentages.
You are taking 80% (0.8) of 0.5. So 80% is less than 100%, therefore you will only get a fraction of 0.5, making it smaller. Any time you multiply a number by less than one (identity) you will make the number smaller.
8 x 1.5 = 12
17.1
five ninths times eight is forty ninths.
Zero point seven five eight.
I would write it as: eight, point, sixty-five. Or eight, point, six five.
A negative four point five; that is: -4.5
68.3
30.25
Five point zero eight.
It is five and five hundred seventy-eight thousandths, or five point five seven eight.
Eight times twenty-five times twenty-three is equal to 4,600.
Seven point thirteen ie eight point three.