ANSWER:
170 liters of 10% hydrochloric acid must be mixed with 1700 liters of 65% hydrochloric acid solution to obtain 1870 liters of 60% solution.
SOLUTION:
First, set up a table. Fill in the unknowns with variables x and y. The table is attached below
From this, we can easily set up the two equations. Â
Sum of values of two acids = Value of mixture Â
0.1x + 0.65y = 1122 Â
For convenience, we'll multiply the entire equation by 100,
10x + 65y = 112200 Â ------ (1) Â
Now, Sum of amounts of each acid = Amount of mixture Â
x + y = 1870 Â ---------(2)
multiply (2) with 10 for easy calculation and derive the equation into one variable.
10x + 10y = 18700 Â
Subtracting equation (2) from (1), Â
( + ) 10x + 65y = 112200
( − ) 10x + 10y = 18700
we get the solution as,
0 + 55y = 93500
Thus, 55y = 93500
y = 1700
Substituting y = 1700 in (2),
x + 1700 = 1870 Â
x  = 1870 - 1700 Â
x  = 170 Â
So, we have x = 170 and y = 1700
We can conclude that 170 liters of 10% hydrochloric acid must be mixed with 1700 liters of 65% hydrochloric acid solution  to obtain 1870 liters of 60% solution.