Question 487869
Jack travels from A to B at 30 mph, and returns at 10 mph.
Jill leaves at the same time as Jack, and travels from A to B and back at a constant speed of 20 mph.
 Who gets back first?
:
let d = the one way distance
let a = Jack's average speed for the round trip
:
write a time equation
{{{d/30}}} + {{{d/10}}} = {{{(2d)/a}}}
Multiply by 30a
da + 3da = 30(2d)
da + 3da = 60d
Simplify divide by d
a + 3a = 60
4a = 60
a = {{{60/4}}}
a = 15 mph av speed, obviously, Jill will get back first