Final answer:
By using the ratio of 4:25 and the total class size of 18, we calculate a part value of 18/29 and determine that there are roughly 15.5 girls, so we round down to conclude there are 15 girls in Mrs. Chong's fifth-grade class.
Step-by-step explanation:
To calculate the number of girls in Mrs. Chong's fifth-grade class, we need to use the ratio of boys to girls provided, which is 4:25. Since the total number of students in the class is 18, we can set up a proportion where the sum of the parts of the ratio equals the total number of students. In this case, 4 parts for boys plus 25 parts for girls equals 29 parts in total. To find the value of each part, we divide the total number of students, 18, by the total number of parts, 29.
Let's call each part 'x'. So, 4x + 25x = 18. Solving for 'x' we get x = 18 / 29. The number of girls is 25 times 'x', which we calculate as 25 x (18 / 29). When we do this calculation, we get approximately 15.5, but since we can't have half a student, we conclude that there must be 15 girls in the class, rounding down to the nearest whole number.