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Answer 1 · 2018-03-01T01:48:42

7.5 litres of 10% acid
22.5 litres of 30% acid

Let the amount of 10% acid added is #x# litres.
Then the amount of 30% acid added is #(30-x)# litres.

Total amount of acid "molecules"
#=30*25%#
#=7.5# litres.

#x*10%+(30-x)*30%=7.5#

#10x+900-30x=750#

#-20x=-150#

#x=7.5#

Therefore a total of 7.5 litres of 10% acid is added, and we can get
#(30-7.5)=22.5# litres of 30% acid.