Can you show me how to work this out?

Question

In 2000, a record number of music CDs were sold in the U.S.. By 2005, this number had been decreased to 705.4 million music CDs. If this represented a decrease of 25%, the number of music CDs sold by the U.S. In 2000.

Answer 1

Hi Rebecca,

 

Let's begin by assigning a letter to represent our unknown:

    x = # of music CDs sold in 2000

 

We are told that 705.4 million CDs were sold in 2005 and that number represented a 25% decrease from the number sold in 2000.  We can express this relationship by this equation:

    x - 0.25x = 705.4 (25% = 25/100 = 0.25)

 

Solving our equation for x:

    x - 0.25x = 705.4 (our equation)
    0.75x = 705.4

    x = 705.4/0.75

    x = 14108/15

    x = 940 and 8/15 million music CDs sold in 2000

 

We can verify our answer by plugging it back into our equation and seeing if both sides prove true:

    x - 0.25x = 705.4 (our equation)

    14108/15 - 0.25(14108/15) = 705.4

    14108/15 - 3527/15 = 705.4

    10581/15 = 705.4

    705.4 = 705.4 (both sides proven true)

 

Since both sides of our equation have been proven true, we are confident that our answer is correct. 

 

Thanks for submitting this problem and glad to help.

 

God bless, Jordan.

Answer 2

x=# of CDs sold in 2000

(x-705.4)/x=25%

(x-705.4)/x=25/100

cross multiply

100x-70,540=25x

100x-25x=70,540

75x=70,540

x=70,540/75

x=940.53 million CDs sold in 2000

check:

940.53-705.40=235.13

235.13/940.53=0.2499973=24.99973% or approximately 25 %