In a class, 60% of students are from India and 50% of the students are girls. If 30% of the Indian students are girls, then what percentage of foreign students are boys?

The correct option is 20%.

Let us solve this problem step-by-step by assuming a total number of students in the class.

Step 1: Assume the total number of students in the class.

Let the total number of students in the class be $100$.

Step 2: Calculate the number of Indian and foreign students.

It is given that 60% of the students are from India.

Number of Indian students = $60\%\text{of}100=60$

The remaining students are foreign students.

Number of foreign students = $100-60=40$

Step 3: Calculate the overall number of girls and boys in the class.

It is given that 50% of the students are girls.

Total number of girls = $50\%\text{of}100=50$

Total number of boys = $100-50=50$

Step 4: Find the number of Indian girls and Indian boys.

It is given that 30% of the Indian students are girls.

Number of Indian girls = $30\%\text{of}60=\frac{30}{100}\times 60=18$

Number of Indian boys = $60-18=42$

Step 5: Find the number of foreign boys.

Since the total number of boys in the class is 50, and 42 of them are Indian boys:

Number of foreign boys = $\text{Total boys}-\text{Indian boys}$

$\text{Number of foreign boys}=50-42=8$

Step 6: Calculate the percentage of foreign students who are boys.

We need to find what percentage of the foreign students ($40$ in total) are boys ($8$ in total).

$\text{Percentage of foreign students who are boys}=\left(\frac{8}{40}\right)\times 100=20\%$

Thus, 20% of the foreign students are boys.