The answer is the option C and the option D, which are:
C. Double the number of pages in the book.
D. The age of my friend.
The explanation for this problem is shown below:
By definition, a variable is an unkown quantity. In the Option A the quantity is given: 
seconds in a minute. In the option B you know the quantity too, which is 
years old. But the option C and the option D does not give any quantity, you don't know the number of pages in the book or the age of the friend yet. Therefore, the answer is the options C and D.
Step-by-step explanation:
this month-100 percent
then previous month 100-20=80 percent
so
if 48=100percent
then x=80percent
x=(80×48)/100
x=38.4 ≈ 38 pairs if shoes
Answer:
false
Step-by-step explanation:
Find the standard form of the equation of the parabola with a focus at (-4, 0) and a directrix at x = 4.
