To find the probability of a moth being black, you need to use the formula:
\[ \text{Probability} = \frac{\text{Number of black moths}}{\text{Total number of moths}} \]
In this case, the number of black moths is 35, and the total number of moths is:
\[ 50 \text{ (brown)} + 15 \text{ (yellow)} + 35 \text{ (black)} = 100 \]
Now, plug in the numbers:
\[ \text{Probability} = \frac{35}{100} = 0.35 \]
To convert this to a percentage, multiply by 100:
\[ 0.35 \times 100 = 35% \]
Thus, the probability of a moth being black is 35%.