Question 823038
Assign Variables:
v = How many liters of 40% acid 
L = 40%, the low concentration of acid
R = 10 liters of 65%, higher concentrated acid
H = 65% the higher concentration acid
T = 45%, the target concentration of acid wanted


{pure amount of acid}/{amount of blend}={resulting concentration}


{{{Pure Acid = L*v+H*R}}}, which is 100 times larger because direct percents are used;


{{{Amount of Blend = v+R}}}


Equation to solve:
'
{{{(Lv+HR)/(v+R)=T}}}
Solve for the UNKNOWN variable, v.
Replace all other variables with their given values and compute v.