Question 816565
This depends on the kind of percent concentration: either w/v or v/v.
This help will be according to percents as volume per volume.


u = how much 40%


{{{(40u+80*10)/(u+10)=65}}}

Solve for u.

{{{8u+160=13(u+10)}}}
{{{8u+160=13u+130}}}
you can finish?