To solve this problem, we need to calculate the probability that all 3 selected students are girls, given that there are 15 boys and 10 girls in the class.

Step-by-step solution:

1. Total number of students:
   The total number of students in the class is:
   $15 \, (\text{boys}) + 10 \, (\text{girls}) = 25 \, (\text{students})$

2. Total number of ways to select 3 students from 25:
   The number of ways to select 3 students from 25 can be calculated using the combination formula: $\binom{25}{3} = \frac{25 \times 24 \times 23}{3 \times 2 \times 1} = 2300$

3. Number of ways to select 3 girls from 10:
   The number of ways to select 3 girls from 10 can also be calculated using the combination formula: $\binom{10}{3} = \frac{10 \times 9 \times 8}{3 \times 2 \times 1} = 120$

4. Probability that all 3 selected students are girls:
   The probability is the ratio of favorable outcomes (selecting 3 girls) to the total outcomes (selecting 3 students from the class): $P(\text{all girls}) = \frac{\binom{10}{3}}{\binom{25}{3}} = \frac{120}{2300} = 0.05217$

5. Convert to percentage:
   To express the probability as a percentage, multiply by 100: $0.05217 \times 100 = 5.217\%$

Final Answer:

The probability that all 3 selected students are girls is approximately 5.22%.

Would you like more details or have any questions?

Here are 5 related questions:

1. How would the probability change if 4 students were selected?
2. What is the probability of selecting 2 boys and 1 girl?
3. What is the probability of selecting 3 boys?
4. How many different ways can 2 boys and 1 girl be selected?
5. What is the probability of selecting at least 1 girl?

Tip: When calculating probabilities involving selections, always consider using combinations when the order of selection does not matter.