First, let's write this as a decimal!
1st digit after decimal: tenths
2nd digit after decimal: hundredths
3rd digit after decimal: thousandths
4th digit after decimal: ten thousandths
"Ten thousandths" means the given digit, in this case the 9, is four digits after the decimal.
9 ten thousandths as a decimal is 0.0009
Scientific notation has two parts:
The first part is a number greater than or equal to one and less than 10. For example: 3, 4.459, 9.9
The second part is that first number multiplied by 10^x, where x is an integer that changes the decimal place of the first number. Remember that each time you multiply by 10, the decimal place moves to the right once. So if you multiply by 10 five times (10^5), then the decimal moves to the right five times.
To convert a number into scientific notation, find the first non-zero number (in this case 9). Then, if there are digits after that number, place a decimal point after it and write the remaining digits (in this case we do nothing because we are only given a single 9).
At this point, we have 9.
Now count how many digits away the decimal is from the given decimal. Remember that 9 still has an implied decimal to the right of it (9.). For 9 to become 0.0009, we have to move the decimal place after the 9 four places to the left. This is the same as dividing by 10 four times, or multiplying by 10^-4.
Final answer is 9 x 10^-4
