Let x be the required amount (volume) of the 20% acid solution (in milliliters).
Then the equation for the pure acid volume is
0.2x + 0.40*50 = 0.25*(x + 50).
It is your basic equation for this problem.
Simplify it
0.2x - 0.25x = 0.25*50 - 0.4*50
Express x from the equation and calculate the answer
x = = 150.
Answer. 150 milliliters.
CHECK. (0.20*150 + 0.40*50)/(50 + 150)}}} = 0.25, or 25%. ! Correct !
Solved.
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