Question 591392
A chemistry student needs to make a solution that is 70% water and 30% hydrochloric acid. The student's current mixture of 300 mL is 60% water and 40% hydrochloric acid. How much water must the student add to achieve his desired solution? 
-------
Equation:
water + water = water
------
0.60*300 + x = 0.70*(300+x)
-----
Multiply thru by 100 to get rid of the decimals.
-------------
60*300 + 100x = 70*300 + 70x
30x = 10*300
x = 100 mL (amt of water to add)
======================
Cheers,
Stan H.
===============