A chemist needs a solution of tannic acid 70% pure. How much distilled water must he add to 5 gallons of acid which was 90% pure to obtain the 70% solution?

30; If you add and subtract these numbers you should get 30%

Answer: 1.4286 gallons

Step-by-step explanation: the equation would be:

0.9*5+0x=0.7 (5+x)

then you can shorten it down to:

4.5=3.5+0.7x

subtract both sides by 3.5 and you end up with:

1=0.7x

divide both sides by 0.7 and you get 1.4286 gallons