Question 213292
Let {{{x}}}= gallons of 4% acid solution to be added
In words:
(gallons of acid) / (gallons of solution) = 7%
given:
{{{.04x}}} = gallons of acid in 4% solution
{{{.13*30 = 3.9}}} = gallons of acid in 13% solution
{{{30 + x}}} = gallons of 7% solution
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{{{(.04x + 3.9) / (30 + x) = .07}}}
{{{.04x + 3.9 = .07*(30 + x)}}}
{{{.04x + 3.9 = 2.1 + .07x}}}
{{{.03x = 3.9 - 2.1}}}
{{{.03x = 1.8}}}
{{{x = 60}}}
60 gallons of 4% acid solution need to be added
check answer:
{{{(.04x + 3.9) / (30 + x) = .07}}}
{{{(.04*60 + 3.9) / (30 + 60) = .07}}}
{{{(2.4 + 3.9) / 90 = .07}}}
{{{6.3 / 90 = .07}}}
{{{6.3 = 6.3}}}
OK