The volume of 70% solution used will be 20 liters. Option A is correct.
What is the percentage?
The quantity of anything is stated as though it were a fraction of a hundred. A fraction of 100 can be used to express the ratio.
Let x is the volume when the 70% solution is used and the volume of the 2 nd acid solution is x₂
If the total volume of the first acid solution is 50
v₁+v₂= 50
x₁+x₂=50
x₁=50-x₂
A 20% acid solution is mixed with a 70% acid solution to get 50 liters of a 40% solution;
⇒v₁x₁+v₂x₂=vx
⇒0.2(50-x)+0.7(x)=0.4(50)
⇒10-0.2x+0.7x=20
⇒10+0.5x=20
⇒0.5x=10
⇒x=20
The volume of 70% solution used will be 20 liters.
Hence option A is correct.
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