QUESTION:
The equation              LAMBDA = 5673 - 34 t   
gives the wavelength of some light in nanometers
as a function of the time t in seconds.  (LAMBDA written as a greek letter.)

What is the wavelength at t = 123 seconds?

ANSWER:
Don't worry about the fact I never discussed Greek letters or nanometers
or wavelength of light!  Those are red herrings.  Only thing that matters
is that something (wavelength LAMBDA) is a function of something else 
(time t).
Answer:  
LAMBDA = 5673 - 34 * 123 =   1491.


QUESTION: How long before wavelength reaches 3055 nm?
ANSWER: solve   3055 = 5673 - 34 t
for t.  Get t = (5673-3055)/34 = 77.



QUESTION:
If the price of gasoline changes with time, what is the
INDEPENDENT VARIABLE and the DEPENDENT VARIABLE?

ANSWER:
The DEPENDENT variable (another name for the OUTPUT of the
function) is the price of gasoline.
The INDEPENDENT variable (another name for the INPUT of the
function) is the time.

OTHER FACTS about functions: the SET of possible inputs is the DOMAIN.
The set of possible outputs is the RANGE. A FUNCTION is a machine
that eats an input and spits out an output.  You can specify a
function
   YourFunctionName(x)
by describing how it computes an output from the input x. That
description could be words, graphs, cases, or formulae.
For example
   F(x) = 3x+5   
would be a function named F, that eats input x, spits
out 3 times x, plus 5. Its domain is all real numbers. So is its range.
   G(t) = 7/t
would be a function named G, that eats input t, spits
7/t. Its domain is all NONZERO real numbers. So is its range.


QUESTION:
Is the price of bulldozers a function?
ANSWER: No, not the way it is said here.
To have a function there has to be an input variable (such as time)
specified.  It WOULD be a function of time if that had been said
(assuming there were some way to tell the price at each time). But
for all one can tell from this wording, it was intended it be a function of what
country you are in!  Of of your age!  Or not a function of anything!




QUESTION:                              50
What is   1 + 3 + 9 + 27 + 81 + ... + 3   ?

ANSWER:                                               2   3        n
The sum of exponentially growing quantities  1 + c + c + c  +...+ c
is given by                n+1
                          c - 1
                    sum = -----
                          c - 1.
Here c=3 and n=50 so we get
          51
        (3  - 1)/2.

It is a good idea to SANITY CHECK this formula by trying n=0, n=1, n=2
and verifying you get the right answers
                                         1,  1+3=4,  and 1+3+9=13.
(Watch out for n=0 versus n=1 as the "first" term!!  
Remember           0
                  x  = 1.)
If it is a multiple choice test and they gave you a choice
of several formulas, one of which was the above, sanity checking
in this way might be the easiest way to solve the problem.
You can rule out the wrong, insane answers one by one.