Davis Middle School prides itself on the fact that 120 of its 300 students are enrolled in Band. The band director would like to take the band to a competition on Tuesday, which is the day that the Humanities class is having a chapter test. If the director chooses a band member at random, there is a 30% chance that the chosen student is also enrolled in Humanities this term. What is the probability that a Davis student selected at random is enrolled in both Humanities and Band?

A. 0.12

B. 0.28

C. 0.30

D. 0.36

Get a ruler in your hands. Measure things until you start to understand how a ruler works. Measure some stuff and figure out where the center is. Say you measure a book and it's 7/8" thick. You look at your ruler and see that every eighth is divided into two sixteenths, so obviously half of 7/8" is going to be 7/16". If you write that out you have 1/2 x 7/8 = 7/16. And you notice that 1/2 is divided into 2/4 and then into 4/8 and so on, so you can convert anything to anything by multiplying all the numbers on top and then all the numbers on bottom.

Other rulers are divided into 10 and 100 parts. But an inch is still an inch, so anything on one ruler can be translated to the other ruler. A half inch on one ruler is 5/10 or 50/100 on the other. An eighth inch is just 12.5 marks when you have 100 marks per inch. A metric ruler divides an inch into 25.4 parts, so a half inch would be 12.7 of those parts. Pretty simple, isn't it? Practice this a bit and people will think you went to wizard school.

Percent is simply a ruler with 100 marks. The only confusion is trying to keep track of what the marks represent, since that changes from time to time.

30% of the band are in humanities. That equals 0.3 x 120 = 36 students. Then 36/300 x 100% = 12% probability.