[nomadmba]

Here are three questions that have left me scratching my head. I have the answers, but not the methodology:

1. For which of the following functions is f(a+b)= f(a) + f(b) for all positive numbers a and b?

a. f(x) = x*x
b. f(x) = x + 1
c. f(x) = sq. root of x
d. f(x) = 2/x
e. f(x) = -3x


2. In the XY plane, at what two points does the graph of y= (x+a)(x+b) intersect the X axis?
1) a + b = 1
2) the graph intersects Y axis at (0, -6)

3. There are 12 temp emloyees in a company. 4 of them will be hired at permanent staff. If 5 of 12 of the temp staff are women, how many of the possible groups of 4 temp employees can consist of 3 women and 1 man?

I know the last should be fairly simple but my mind just doesn't seem to process permutation and combination questions...

Thanks.