Question 869337
y = length of short piece
x = length of long piece
w = length of whole original piece, w=12.
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Write every numeric statement that you can about this problem.
x=y+3, from description.
x+y=w, from description, sum of the pieces must be equal to the whole original.
The question asks for length of short piece, here chosen as variable, y.  You have two equations and the unknown variables are x and y.


Solve the system for y; use substitution.
{{{x+y=w}}}
{{{y+x=w}}}
{{{y+(y+3)=w}}}, the substitution
{{{y+y+3=w}}}
{{{2y+3=w}}}
{{{2y=w-3}}}
{{{highlight(y=(w-3)/2)}}}


You were given that w=12, so you continue, {{{y=(12-3)/2}}},
{{{y=4&1/2}}}.