Question 1106175
4%  is  {{{4/5}}} of 5%.

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{{{40*5/(40+v)=4}}}


{{{50/(v+40)=1}}}


{{{50=v+40}}}


{{{v=50-40}}}


{{{highlight(v=10)}}}, amount volume of neutral material to add




NOTE:  {{{40/(10+40)=40/50=highlight_green(4/5)}}}