I'm confused with some high school level algebra, help please?

I have the answers, but I'm just not sure how to get to that. I'm hoping some one can explain to me.

1)Three people who work full time are to work together on a project, but their total time on the project is to be equivalent to that of only one person working full time. If one of the people is budgeted for _ of his time to the project and a second person for 1/3 of her time, what part of the third worker’s time should be budgeted to this project?

-answer is 1/6. I dont understand this either. I thought it was 1/3. since 3 people using 1/3 each of their time would equal 1 full time? I have no idea why there is a "_" in the question.

2)Simplify: 1/-2^-2

-answer: is -4. since the denominator has the power of a negative it rids of the numerator's existance. So what is left is just -2^2.... right? making 4 not - 4, since two negatives is positive... yes? no?

3)solve for x if: 1/x + 2/y = 3/z

-answer: -zy/2z-3y or zy/3y-2z

so I know what I do in this is isolate the 1/x from the rest and some how get rid of the numerator of 1, but I'm not sure how to do that. Or if thats even the correct method.

4)If ((3/2)x) + 4 = 10, find the value of ((5/8)x) - 2

-answer is -7/6. in the first one i solved for x which turns out to be 4 and then I replace 4 into the x of the second equation which turns out to be 1/2. and it turns out I was complete wrong.

Questions are from http://www.pasadena.edu/studentservi...s/MathSamp.pdf

I can't do most of the questions in the last page. Never took pre cal. (Thinking)