Question 127355
Let {{{a}}} = amount of 30% acid solution needed
Let {{{b}}} = amount of 55% acid solution
Given is {{{b = 8}}}liters
(acid in 30% and 55% solutions)/(total solution) = 40%
{{{(.3a + .55b) / (a + b) = .4}}}
{{{(.3a + .55*8) / (a + 8) = .4}}}
{{{.3a + 4.4 = .4(a + 8)}}}
{{{.3a + 4.4 = .4a + 3.2}}}
{{{.1a = 1.2}}}
{{{a = 12}}}liters
12 liters of the 30% solution must be added
check:
{{{(.3*12 + .55*8) / 20 = .4}}}
{{{3.6 + 4.4 = 20*.4}}}
{{{8 = 8}}}
OK