Answer: There were 10 students in the class on the first day.
Step-by-step explanation:
Let x be the number of students of the first day.
Given: A college writing seminar increased its size by 50 percent from the first to the second day.
i.e. Number of students on second day = (Number of students on first day)+(50% of Number of students on first day)
= x +50% of x
= x+0.50x
= (1.50)x
=1.50x
Since, it is given that the total number of students in the seminar on the second day was 15.
i.e. [tex]1.50x=15[/tex]
[tex]\Rightarrow\ x=\dfrac{15}{1.5}\Rightarrow\ x=\dfrac{150}{15}\\\\\Rightarrow\ x=10[/tex]
Hence, there were 10 students in the class on the first day.