Just basic math can some one please explain it to me

The unit cost of pens is the same regardless of how many pens are purchased. If the cost of P pens is D dollars, what is the cost, in dollars, of X pens?
A) XD
B) XPD
C) XD/P
D) XP/D
E) PD/X

I don't understand the question itself. What in the world is X ! And what are they looking for?
I tried 1 pen is for 2 dollars but I didn't get it. This looked so easy at first, it makes me feel stupid.

the question is asking you how much X amount of pens cost:
X = could be any amount of pens
D = total cost of P pens (not the total cost of X pens!)




===your example===
if you have 1 pens and you payed 2 dollars in total, then the unit cost is:
2/1 dollars
= 2 dollars

so if each pen costs 2 dollars, then 5 pens costs:
5 * 2 dollars
= 10 dollars

coincidentally this also works with (C) and (A) because you picked P = 1:
XD/P = XD/1 = XD

dividing by 1 makes P have no effect.
try to test with numbers that always have an effect.
they are still different formulas.
different formulas sometimes have the same answer.
try a different number for P and it probably won't work.



===your question===
if you have P pens and you payed D dollars in total, then the unit cost is:
D/P dollars

so if each pen costs D/P dollars, then X pens cost:
X * D/P dollars
= XD/P dollars

if P pens cost D dollars, then the unit cost (dollars per pen cost) is: D / P

that represents the cost for each pen.

If you buy X pens (X means the number of pens you buy)

then the total cost is (D/P) * X = XD/P (how your choices are arranged)

multiplication is commutative.

id est

X is a hypothetical number of pens. It's the same as P. If you replace P with X, what equation do you have?

P pens cost D $

So 1 pen costs = D / P

So X pen costs = D / P x X= XD/ P

Answer is C)

P stands for Pair
so 1 Pair of pants cost $D
x = the number of pair of pants you are buying
a)XD means you are buying some number of pants for D dollars each

The question says X is the number of pens to be purchased.
Cost of 1 pen = D/P
Cost of X pens = XD/P
Answer C)

X is the number of pens you will buy