The percent decrease is (the amount of decrease)/(original amount) the amount of decrease is $50-5=45$ so the percent decrease is $\frac{45}{50}$ which is ~$ 90 \textbackslash\%$ 
The average cost of a long-distance call in the USA in 1985 was 50 cents per minute, and the average cost of a long-distance call in the USA in 2008 was 5 cents per minute. Find the approximate percent decrease in the cost per minute of a long- distance call. (adapted from 2007 AMC 8, Question \#6) 
(1) $$30$$ 
(2) $$40$$ 
(3) $$50$$ 
(4) $$80$$ 
(5) $$90$$ 