rupsk wrote:The cost of 1 unit of electricity during a 4 year period is given below. Year 1, $1 per unit. Year 2, $1.5 per unit. Year 3, $1.2 per unit. Year 4, $2 per unit. If a factory spent equal dollars each year for electricity what was the average cost of a unit of electricity during the 4 year period?
A. $ 1.333
B. $1.250
C. $1.425
D. $1.175
e. $1.500
my answer was c but correct ans is a. please help to understand my mistake.
Here is my take:
Total cost year 1 = 1X
Total cost year 2 = 1.5Y
Total cost year 3 = 1.2Z
Total cost year 4 = 2M, Where, X, Y, Z, and M represent the units of electricity purchased in year 1, year 2,year 3, and year 4 respectively.
As stated in the question, 1X = 1.5Y = 1.2Z =2M
And let's represent them all by another variable 'a'
Hence, to get the weighted average, add all the cost and divide that by the sum of X, Y, Z, and M.
1X + 1.5Y + 1.2Z + 2M = a + a + a + a = 4a so this is our numerator.
Now let's find X,Y,Z, and M.
1X=a
X=a
1.5Y= a
Y=2a/3
1.2z = a
z= 5a/6
2m = a
m= a/2
Therefore, the weighted average is equal to: (4a)/[a +(2a/3)+ (5a/6) + (a/2)]
= 4a/3a = 1.333..
But, I feel that the question should have asked for the
approximate value as there is no value from the choices that's equal to our answer. Or is the measurement of the dollar a discrete variable? If that is so, then Ok. Hahaha....
