During a trip, Francine traveled x percent of the total distance at an average speed of 30 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?
Answers:
A) (180-x)/2	B) (x+60)/4	C) 4800/x+100	D) 600/(115-x)	E) 12,000/(x+200)
total distance =100 ;total time = T   t1 = x/30 t2 = 100-x /60   T =t1+t2 = x/30 + 100-x/60 = (60x + 3000- 30x)/1800   = (30x+3000)/1800   = x +100 / 60   av speed = 100*60/x+100 = 4800/x+100   4800/x+100
<result>C</result>
During a trip, Francine traveled x percent of the total distance at an average speed of 30 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?