ACT Math: Probability

SAT Question of the Day

The SAT question of the day is a Coordinate Geometry Question that has already been addressed on this blog: click here to see an explanation.

ACT Question of the Day

Today's SAT math question tests your understanding of probability.  Remember that a probability is just a fraction that puts the number of relevant outcomes over the total number of possible outcomes.

Your question tells you that there are 14 total balloons: 9 yellow, 3 red, and 2 green.  If one yellow balloon is sold, what is the probability that the next balloon sold will also be yellow?  

Start by setting up the original probability, before anything is sold.  The only balloons that you care about, the only ones that are relevant, are yellow.  Put 9 yellow balloons on the top of a fraction.  How many total balloons are there?  14!  The probability of selling a yellow balloon is 9/14.

Don't stop there!  That was before one yellow balloon was sold!  You need to get rid of that balloon from this fraction by taking one away.  Now there are only 8 balloons left.  Make sure you notice that if you take one yellow balloon away, you are also taking away one balloon from the total of 14.  There are now only 13 balloons total.  Your fraction is now 8/13.  This fraction represents the probability that the next balloon sold will be yellow.

The correct answer is (A).

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