<PRE><B>Question 306261</B>
A dump truck is hauling debris at a mining site. on its first trip it hauls away 360 tons of rubble; 
on its second trip it hauls away 300 tons of rubble.
if it hauls an average of 350 tons of rubble for all three trips,
 how much rubble did it haul on its last trip?
:
Using your correct equation:
{{{(360+300+x)/3}}} = 350
Multiply by 3 to get rid of the denominator
360 + 300 + x = 3(350)
660 + x = 1050
x = 1050 - 660
x = 390   </PRE>