Question 1144529
x of 75% copper
750-x of 35% copper


{{{75x+35(750-x)=60*750}}}

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{{{75x+35*750-35x=60*750}}}
{{{75x-35x=60*750-35*750}}}
{{{x(75-35)=(60-35)(750)}}}

{{{highlight_green(x=(750(60-35))/(75-35))}}}

{{{x=750(25/40)}}}

{{{x=750(5/8)}}}