Answer:
3999999999/100000000
Explanation:
To write 39.99999999 as a fraction you have to write 39.99999999 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.
39.99999999 = 39.99999999/1 = 399.9999999/10 = 3999.999999/100 = 39999.99999/1000 = 399999.9999/10000 = 3999999.999/100000 = 39999999.99/1000000 = 399999999.9/10000000 = 3999999999/100000000