<PRE><B>Question 587747</B>
Jake is on a 24-mile bike trip. He wants to average 10 miles per hour.
 He is halfway to his destination and has averaged 8 miles per hour.
 What must his average speed be on the last part to complete on time
;
Let s = the required speed to average 10 mph for the trip
:
write a time equation, time = dist/speed
:
{{{12/8}}} + {{{12/s}}} = {{{24/10}}}
Multiply by 40s
40s*{{{12/8}}} + 40s*{{{12/s}}} = 40s*{{{24/10}}}
cancel the denominators
5s(12) + 40(12) = 4s(24)
60s + 480 = 96s
480 = 96s - 60s
480 = 36s
s = 480/36
s = 13{{{1/3}}} mph on the last half of the trip
:
:
Check, find the times.
{{{12/8}}} + {{{12/13.33}}} = {{{24/10}}}
1.5 + .9 = 2.4</PRE>