<PRE><B>Question 997465</B>
1/4 journey at 25 km/h 1/3 at 30km/h and rest at 50km/h.
find average speed
:
Let a = the average speed
We can make this easy, choose a convenient value for the distance of the trip
Dist = 120 km
them
{{{1/4}}}*120 = 30 km
{{{1/3}}}*120 = 40 km
and
50 km = the remainder of the trip
:
Write a time equation; time = dist/speed
{{{30/25}}} + {{{40/30}}} + {{{50/50}}} = {{{120/a}}} 
Multiply equation by 150a, cancel the denominators and you have
6a(30) + 5a(40) + 3a(50) = 150(120)
180a + 200a + 150a = 18000
530a = 18000
a = 18000/530
a = 33.96 ~ 34 km/hr is the average speed</PRE>