"A chemist is using 336 millilitres of a solution of acid and water."
This sentence implies that the solution only contains acid and water.
Now, we are told:
"15.6% of the solution is acid."
What is 15.6% percent though, as a decimal?
Well, 15.0% is actually equal to 0.15 as a decimal. 0.6% is actually 3/5 of 1%, which in turn is 3/5 of 0.010 which is 0.006 as a decimal.
So, we now know that 15.6% is actually equal to 0.156 as a decimal.
Let's multiply 0.156 by 336 to get our answer.
0.156 x 336 = 52.4 (rounded to the nearest tenth)
There are 52.4 millilitres (to the nearest tenth) of acid in the solution.
