Answer:
74%
Step-by-step explanation:
We have been given that the Average cost of a long distance call in the USA was 31 cents per minute in 1978 and 8 cents in 2008.
We will use percent decrease formula to solve our given problem.
[tex]\text{Percent decrease}=\frac{\text{Initial}-\text{Final}}{\text{Initial}}\times 100\%[/tex]
[tex]\text{Percent decrease}=\frac{31-8}{31}\times 100\%[/tex]
[tex]\text{Percent decrease}=\frac{23}{31}\times 100\%[/tex]
[tex]\text{Percent decrease}=0.741935483\times 100\%[/tex]
[tex]\text{Percent decrease}=74.1935483\%[/tex]
[tex]\text{Percent decrease}\approx 74\%[/tex]
Therefore, there is an approximate 74% decrease in cost per minute for the long distance call from 1978 to 2008.
