Final answer:
To find the number of students good at science, multiply the proportion of students good at science by the total number of students.
Step-by-step explanation:
To find the number of students good at science, we need to calculate 50% of the total number of students. Since 50% represents the proportion of students good at science, we can multiply it by the total number of students to get the answer.
Number of students good at science = 50% x 20 students = 0.5 x 20 = 10 students.