Why would you want to use note cards rather than several pages of paper when giving a speech? which of these answers best represents?

A. The audience doesn't like to hear paper rustling.
B. You can color-code note cards.
C. Note cards force you to look at the audience more.
D. Note cards are smaller and easier to handle.

Raul has one solution that is 20% acid by volume and one solution that is 50% acid by volume. he plans to mix together some of each solution to create 30 milliliters of a solution that is 40% acid by volume. how many milliliters of the 20% acid solution should raul use to create the 40% acid solution? can someone explain this to me? i know that the answer is 10 milliliters, but i don't know how to get it.