Question 310697
Evan drove halfway home at 20 miles per hour then sped up and drove the rest of the way at 30 miles per hour.
what was his average speed for the entire trip?
:
let a = average speed for the entire trip
:
Let d = half way distance
then
2d = entire trip
:
Write a time equation
time at 30 + time at 20 = total time
{{{d/30}}} + {{{d/20}}} = {{{(2d)/a}}}
multiply by 60a, results:
2a(d) + 3a(d) = 60(2d)
:
2ad + 3ad = 120d
:
simplify, divide by d
2a + 3a = 120
5a = 120
a = {{{120/5}}}
a = 24 mph is the av speed