If a pipe can fill a tank in x hours, what fractional part of the tank will be filled in one hour? Let's look at a bunch of particular cases when we have a number instead of the letter "x": Case 1: If a pipe can fill a tank inhour, what fractional part of the tank will be filled in one hour? Answer: th of it. [That's 1, or 100%, or all of it] Case 2: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: of it. Case 3: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: rd of it. Case 4: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: th of it. Case 5: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: th of it. Case 6: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: th of it. Case 7: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: th of it. ... Now that list can go on forever and ever. But look at what is always true in every case above: If a pipe can fill a tank in a certain number of hours, what fractional part of the tank will be filled in one hour? The answer is always ths of it. So if we replace the words "that certain number" by the letter "x" you could say this about every one of those: Case x: If a pipe can fill a tank in hours, what fractional part of the tank will be filled in one hour? Answer: ths of it. So the answer is . Edwin