To write .189 as a fraction you have to write .189 as numerator and put 1 as the denominator. Now you multiply numerator and denominator by 10 as long as you get in numerator the whole number.
.189 = .189/1 = 1.89/10 = 18.9/100 = 189/1000
And finally we have:
.189 as a fraction equals 189/1000