<PRE><B>Question 334865</B>
A truck driver traveled at 40 mph for the first part of a 646-mile trip,
 then increased his speed to 58 mph for the rest of the trip. 
The entire trip took 13 hours. How many hours are traveled at 58 mph?
:
let t = time traveled at 58 mph
then
(13-t) = time at 40 mph
:
Write a distance equation; dist = speed * time
;
40 mph dist + 58 mph dist = 646 mi
40(13-t) + 58t = 646
:
520 - 40t + 58t = 646
-40t + 58t = 646 - 520
18t = 126
t = {{{126/18}}}
t = 7 hrs at 58 mph
;
:
Check solution by finding the distances
13 - 7 = 6 hrs at 40 mph
40*6 + 58*7 =
240 + 406 = 646</PRE>