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A solution has a percentage concentration of {ansb} % w/v of {chem}. It was made by mixing {millb} mL of solvent and  [[0]] grams of {chem}.

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Given \\[\\text{percentage concentration (w/v)}=\\dfrac{\\text{mass of solute (g)}}{\\text{volume of solvent (mL)}}\\times \\text{100},\\]

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we can substitute our values for percentage concentration and volume of solvent and rearrange to get the value of 'mass of solute (g)'. 

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$\\text{percentage concentration (w/v)}$$=$$\\dfrac{\\text{mass of solute (g)}}{\\text{volume of solvent (mL)}}\\times \\text{100}$
 
$\\var{ansb}  \\text{ % (w/v)}$$=$$\\dfrac{\\text{mass of solute (g)}}{\\var{millb} \\text{ mL}}\\times 100$
 
$\\dfrac{\\var{ansb}  \\text{ % (w/v)}}{100}$$=$$\\dfrac{\\text{mass of solute (g)}}{\\var{millb} \\text{ mL}}\\times \\dfrac{100}{100}$
 
$\\dfrac{\\var{ansb}  \\text{ % (w/v)}}{100}$$=$$\\dfrac{\\text{mass of solute (g)}}{\\var{millb} \\text{ mL}}$
 
$\\dfrac{\\var{ansb}  \\text{ % (w/v)}}{100}\\times \\var{millb} \\text{ (mL)}$$=$$\\dfrac{\\text{mass of solute (g)}}{\\var{millb} \\text{ mL}}\\times \\var{millb} \\text{ mL}$
 
$\\var{gramsb} \\text{ (g)}$$=$$\\text{mass of solute (g)}$
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https://en.wikipedia.org/wiki/Mass_concentration_(chemistry)#Usage_in_biology

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