Which of the following is the independent quantity in the function below?

amount of remaining mp3 player memory(number of downloaded songs)

a.mp3 player
b.amount of remaining mp3 player memory
c.number of downloaded songs
d.total memory of mp3 player

Among the following, the independent quantity in the function:
amount of remaining MP3 player memory as a function of downloaded songs is

C. NUMBER OF DOWNLOADED SONGS

The remaining memory will depend on the number of songs downloaded. So, the number of downloaded songs is considered as the independent variable while the remaining memory is the dependent variable.

Let the cost of a chicken be x and the cost of a duck, y, then

50x + 30y = 550 . . . (1)
44x + 36y = 532 . . . (2)

(1) x 6 ⇒ 300x + 180y = 3,300 . . . (3)
(2) x 5 ⇒ 220x + 180y = 2,660 . . . (4)

(3) - (4) ⇒ 80x = 640
⇒ x = 640 / 80 = 8

From (1): 50(8) + 30y = 550
⇒ 30y = 550 - 400 = 150
⇒ y = 150 / 30 = 5

Therefore, the price of a chicken is $8 and the price of a duck is $5.