80% of the students who attended a concert came from the city. Of these, 70% were girls. If 150 boys came from the city, how many students attended the concert?
First, you must find the percentage of boys who came from the city. Since 70% of students who came from the city were girls, then 30% were boys. Next, you must find how many total students were from the city using the proportion:
# of boys from the city/total students from city = percentage of boys from the city/100
Once you find that, you use this proportion to find the total number of students who went to the concert:
# of students from city/# of students total = Percentage of students from the city/100
Hope this helps :)