Question 195320
Let {{{x}}}= liters of 10% solution needed
In words:
(liters of silver iodide)/(total liters of solution) = 6%
{{{(.04*9 + .1x) / (9 + x) = .06}}}
Multiply both sides by {{{9 + x}}}
{{{.36 + .1x = .06*(9 + x)}}}
{{{.36 + .1x = .54 + .06x}}}
{{{.04x = .18}}}
{{{x = 4.5}}}
4.5 liters of the 10% solution are needed
check:
{{{(.04*9 + .1x) / (9 + x) = .06}}}
{{{(.04*9 + .1*4.5) / (9 + 4.5) = .06}}} 
{{{(.36 + .45) /13.5 = .06}}}
{{{.81/13.5 = .06}}}
{{{.06 = .06}}}
OK