Probability

Have you ever tried to guess what’s for dinner before you smell it? If it’s Friday, there’s a really good chance it’s pizza! 🍕 That "chance" is what mathematicians call probability. Probability is just a fancy way of asking, "How likely is something to happen?"

It’s a huge part of the ISEE, showing up in both the Quantitative Reasoning and Mathematics Achievement sections. We measure probability on a scale from $0$ (no way, like a T-Rex showing up to take your test 🦖) to $1$ (definitely happening, like you doing an awesome job!). Most of the time, probability lives right in the middle as a fraction.

Think of a giant gumball machine. If there are $10$ gumballs and $3$ are your favorite blue raspberry flavor, your chance of getting a blue one is $3$ out of $10$. On the ISEE, we write that as the fraction $\frac{3}{10}$. The bottom number (denominator) is always the total number of things, and the top number (numerator) is the number of winning things!

Sometimes, the ISEE will ask you to figure out the chances of two things happening in a row. Like getting a blue gumball AND rolling a $6$ on a dice. Here is a secret test trick: when you want one thing AND another thing to happen, you multiply their probabilities together! 🎲 Get ready to be a probability pro!