<PRE><B>Question 265478</B>
a car travels 40 mph for 20 miles, 36 mph for 24 miles, and 48 mph for 16 miles. what is its average speed?
:
Total distance 20 + 24 + 16 = 60 mi
Let x = average speed for the 60 mi trip
:
Write time equation, time = dist/speed
:
{{{20/40}}} + {{{24/36}}} + {{{16/48}}} = {{{60/x}}}
Multiply equation by 720x, results
18x(20) + 20x(24) + 15x(16) = 720(60)
:
360x + 480x + 240x = 43200
:
1080x = 43200
x = {{{43200/1080}}}
x = 40 mph average speed
:
:
Check solution in the original time equation
{{{20/40}}} + {{{24/36}}} + {{{16/48}}} = {{{60/40}}} 
.5 + .67 + .33 = 1.5</PRE>