To write 8.57 as a fraction you have to write 8.57 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.
8.57 = 8.57/1 = 85.7/10 = 857/100
And finally we have:
8.57 as a fraction equals 857/100