Question

Use word to write number 7821.8218

Answer 1

Seven thousand eight hundred twenty-one AND eight thousand two hundred eighteen ten-thousandths. In words, "and" always means a decimal point, and that's the only place you say it.

Answer 2

Seven thousand, eight hundred twenty-one and eight thousand, two hundred eighteen ten-thousandths. is the write answer
   IF these numbers are without decimal point
seventy-eight million two hundred eighteen thousand two hundred eighteen