Addition Rule of Probability and Expected Frequency

There are 10 yellow balls out of a total of 50. The probability of drawing a yellow ball is $\frac{10}{50}$, which simplifies to $\frac{1}{5}$.

There are two favourable outcomes (rolling a 2 or a 6) out of 6 possible outcomes. The probability is $\frac{2}{6}$, which simplifies to $\frac{1}{3}$.

The number of red and green marbles is $15+10=25$. The total number of marbles is 30. The probability is $\frac{25}{30}$, which simplifies to $\frac{5}{6}$.

The number of yellow and blue marbles is $2+4=6$. The total number of marbles is 12. The probability is $\frac{6}{12}$, which simplifies to $\frac{1}{2}$.

The probability of rolling a 3 on a fair die is $\frac{1}{6}$. Over 60 rolls, the expected number of times is $\frac{1}{6}\times 60=10$.

The numbers less than 3 are 1 and 2, giving a probability of $\frac{2}{6}$, which simplifies to $\frac{1}{3}$. Over 120 rolls, the expected number is $\frac{1}{3}\times 120=40$.