Question 74219
Let x=distance from 140 lb boy and y=distance from 105 lb boy
{{{140/x=105/y}}}Set up a ratio between the distances and the weights
{{{140y=105x}}}Multiply both sides by xy to get rid of the fraction
{{{x+y=7}}}Here's the sum of the distances
{{{y=7-x}}}Solve for y
{{{140(7-x)=105x}}}plug this into x and solve
{{{980-140x=105x}}}
{{{980=105x+140x}}}
{{{980=245x}}}
{{{980/245=x}}}
{{{x=4}}}
So the 140 pound boy is 4 ft away from the pivot. 
{{{y=7-x}}}
{{{y=7-4}}}
{{{y=3}}}
So the 105 pound boy is 3 ft away.