Question

During a trip, Francine traveled x percent of the total distance at an average speed of 40 miles per hour and the rest of the distance at an average speed of 60 miles per hour. In terms of x, what was Francine`s average speed for the entire trip?A. (1800 - x) /2

B. (x + 60) /2
C. (300 - x ) / 5
D. 600 / (115 - x )
E. 12,000 / ( x + 200)

Answer 1

Correct answer: C. (300 - x ) / 5

Explanation:

Francine traveled x percent of distance at 40 miles per hour and 1-x at 60 miles per hour,

So,

Average speed would be the total distance / the time but in this case we need to calculate an average ponderated speed wich would be

x/100 * 40 + (1 - x/100) * 60 = 40/100 x + 60 - 60/100 x = ( 60 - 20/100 x ) = 60 - 1/5 x = (300 - x) / 5