Answer:
10 videos were sold
Explanation:
Hello There!
First we want to create two equations (system of equations)
let c = CD's sold and v = videos sold
a total of 40 CD's and videos we're sold so
40 = c + v
they we're sold for a total amount of $180 ( $4s per CD and $6 per video) so
4c + 6v = 180
now we are going to solve for number of videos sold sold using eliminations and multipliers
first we want to find a common multiple between 4c and c which would be 4
so we multiply 4c + 6v = 180 by -1 and 40 = c + v by 4
(note we have to choose one of the equations to be multiplied by a negative number because we are trying to eliminate some variables)
-1(4c+6v=180) = -4c - 6v = - 180
4(c + v = 40) 4c + 4v = 160
now we combine the equations
4c -4c cancels out
-6v + 4v = -2v
-180 + 160 = -20
we're left with -2v = -20
then we divide each side by -2
-2v/-2=v
-20/-2=10
so the number of videos sold was 10
now to find the number of CDs sold we plug in 10 into v to one of the equations
40 = c + 10
subtract 10 from each side
40 - 10 = 30
we're left with c = 30
so we can conclude that
30 CDs were sold and 10 videos were sold