SOLUTION: Dmitri needs 7 liters of a 24% solution of sulfuric acid for a research project in molecular biology. He has two supplies of sulfuric acid solution: one is an unlimited supply of t

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Let = liters of 28% solution needed
Let = liters of 14% solution needed
= liters of sulfuric acid in 28% solution
= liters of sulfuric acid in 14% solution
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(1)
(2)
---------------------------
(2)
(2)
(2)
Subtract (1) from (2)
(2)
(1)

and, since
(1)
(1)
(1)
5 liters of 28% solution are needed
2 liters of 14% solution are needed
check:
(2)
(2)
(2)
(2)
(2)
OK