To solve this problem using a double number line, we can start by placing 100 marks on the line to represent the total number of students in the class. Then we can label 15 of those marks as absent students.
Next, we can find the distance between two marks on the line by dividing 100 by the number of marks (in this case, 100/100 = 1). Using this scale, we can find the distance between 15 marks by multiplying 15 by the distance between two marks:
15 marks × 1 = 15
So, 15% of the students are absent, which means that 100% - 15% = 85% of the students are present. We can find the number of students present by multiplying the total number of students (80) by the percentage that are present (85% or 0.85):
80 × 0.85 = 68
Therefore, there are 68 students present in the class on the particular day. We can mark this on the double number line by counting 68 marks from the zero point (where the absent marks start) in the direction of the 100 marks.