1. ## Probabilities Plz Help

hey
1. Probability of tossing at least one head with three coins?
2. Probability of rolling a composite number with one die?

Can someone plz help me asap and explain how they got the answer.

Thanx

2. Originally Posted by ballin_sensation
hey
1. Probability of tossing at least one head with three coins?
2. Probability of rolling a composite number with one die?

Can someone plz help me asap and explain how they got the answer.

Thanx
1. The probability you will have at least one head on three coin flips is equal to 1 minus the probability that you have no heads on three flips. The probability you will have 0 heads on three flips is $\displaystyle \frac{1}{2}\cdot\frac{1}{2}\cdot\frac{1}{2}=\frac{ 1}{8}$. Then the probability of at least one head is $\displaystyle 1-\frac{1}{8}=\frac{7}{8}$. An alternative way is to simply list all possible outcomes and count them or to add the probability of exactly one head ($\displaystyle \left( \frac{3}{8} \right)$, exactly two heads$\displaystyle \left( \frac{3}{8} \right)$, and exactly three heads$\displaystyle \left( \frac{1}{8} \right)$.

2. There are 2 composite numbers on a single dice (4 and 6). Thus, you have a $\displaystyle \frac{2}{6}=\frac{1}{3}$ chance of rolling a composite number.