Question 776513
{{{W[1]*X[1]=W[2]*X[2]}}}
Let's make the son number 1 (and his mother number 2).
{{{W[1]=100}}}{{{lb}}}
{{{X[1]=8}}}{{{feet}}}
{{{W[2]=125}}}{{{lb}}}
{{{X[2]}}}= distance from the fulcrum to the mother
{{{100*8=125*X[2]}}} --> {{{100*8/125=X[2]}}} --> {{{X[2]=32/5}}}
We can also express that as 
{{{X[2]=6.4}}} or {{{X[2]=6&2/5}}}
Or we can say that the mother should sit at 6 feet 5 inches from the fulcrum
{{{6&2/5}}}{{{feet=6feet}}}{{{(2/5)*12inches}}}, but {{{(2/5)*12=4.8=about5}}}, and nobody measures fractions of an inch when playing on a seesaw.