A standard six-sided number cube (die) has the numbers 1 through 6. The even numbers on this cube are 2, 4, and 6.
There are 3 even numbers out of 6 possible outcomes. Therefore, the probability of rolling an even number is:
\[ P(\text{even number}) = \frac{\text{number of even numbers}}{\text{total outcomes}} = \frac{3}{6} = \frac{1}{2} \]
If you roll the die 30 times, the expected number of times you roll an even number can be calculated by multiplying the probability of rolling an even number by the total number of rolls:
\[ \text{Expected even rolls} = P(\text{even number}) \times \text{number of rolls} = \frac{1}{2} \times 30 = 15 \]
Thus, you can expect to roll an even number 15 times.