A scientist has 400 units of a 6% phosphoric acid solution, and an unlimited supply of 12% phosphoric acid solution. How many units of the latter must she add to the former to produce a 10% phosphoric acid solution?	Choose the correct choice
A) 200 B) 400 C) 500 D) 600 E) 800
With mixture problems I usually take following approach   10%=Total mix of acid/Total amount of mixture.   With X= amount of 12% acidic solution we have:   10%=(400*0.06+.12*X)/400+X)   40+0.1X=24+0.12X   16=0.002X   X=800   Answer 800
<result>E</result>
A scientist has 400 units of a 6% phosphoric acid solution, and an unlimited supply of 12% phosphoric acid solution. How many units of the latter must she add to the former to produce a 10% phosphoric acid solution?