In math, numbers can be positive or negative. Negative numbers are less than zero and are denoted by a "" sign in front of the number, such as 10. When adding a positive number to a negative number, the "" merely acts as a minus sign. When multiplying or dividing a negative number to a positive number, the negative sign stays with the answer. Conversely, multiplying or dividing two negative numbers creates a positive number.

Divide 25.5 by 1.5. Set up the division by moving the decimal point one spot to the right, creating 15 divided into 255. Write a negative sign off to the side and circle it boldly to remind yourself that it will be needed later; this will save you from having to carry the negative sign through all of your arithmetic.

Decide how many times 15 goes into the leading two digits of 255. Write down "1" in your answer box. Subtract 15 from 25: 25  15 = 10. Check whether 15 can go into this answer: it can't. Drop down the trailing "5" from the 255 to change the 10 into 105.

Decide how many times 15 goes into 105, taking a guess if you're unsure. Try multiplying 15 by 9: 15 * 9 = 135. Try a lower number since that was too high. Use 7 instead: 15 x 7 = 105. Write "7" in the second spot in the answer box.

Write a negative sign in front of the "17" in the answer box, making it read "17", and you have your answer.