Answer :
Answer:
Initial mass = 25 grams
Step-by-step explanation:
[tex]\left(\frac{x}{x+20}\right)\:=\:\:\left(\frac{x}{x+5}\:-.3\:\right)[/tex]
x = 20 (mass of copper)
[tex]\frac{20}{20+5} = .8 = 80[/tex] percent
[tex]\\\frac{20}{20+15} = .5 = 50[/tex] percent