SAT Math Question of the Day

Math Category: Algebraic Sets:

Q: In a class of 12 students, 7 students watch American Idol, 4 students watch CSI, and 2 watch both tv programs. How many students watch neither tv show?

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5

UNANSWERED.

The correct answer is C.

A: 3 is the right answer.

Let's make a chart to figure out this set problem. There are 12 students in the class, so make the chart 12 columns wide:

1 2  3 4  5 6  7 8  9 10 1112
                 
                 

Next fill in the 7 students watching American Idol:
1 2  3 4  5 6  7 8  9 10 1112
AIAI AIAI AIAI AI       
                 

Next fill in the 4 students watching CSI. Remember that 2 of those students also watch American Idol, so let's say they are student #6 and #7:
1 2  3 4  5 6  7 8  9 10 1112
AIAI AIAI AIAI AI       
       CSI CSICSI CSI    

Now we have filled out the chart with all the information we know. Looking at the chart we see that students #10, #11, and #12 do not watch either American Idol or CSI. So the answer is 3 students watch neither tv show.