Urgent story problem w/ algebra?!

Question

Scientists combined 5 milliliters of a substance containing 2% sandalwood with another substance containing 6% sandalwood to get a substance that contained 5% sandalwood. How many milliliters of the substance containing 6% sandalwood must the chemists have used?

 

if I fail this I don't pass my math lesson D:

Answer 1

The problem looks more difficult than it is because it looks like you have two mystery quantities, but they are related

 

x = amount of second substance

x + 5 = amount of first and second substances combined.

 

(0.02)5 ml + (0.06)x ml  = (0.05)(x+ 5)ml

0.1 ml  + (0.06)x ml = (0.05)x ml + (0.25) ml

(0.06)x ml - (0.05)x ml = (0.25) ml - (0.10) ml

(0.01)x ml = (0.15) ml

x ml = 15 ml