First you must see how many seats were bought. To do this you must make a proportion
80 is a percent and percent's are always taken out of the 100. This means that one proportion will have 80 as the part and 100 as the whole
We want to know what 80% of 2,500 is in order to find how many seats were sold before the show. This means 2,500 is the whole and the unknown (let's make this x) is the part.
Here is your proportion:
Now you must cross multiply
x*100 = 80*2,500
100x = 200,000
To isolate x divide 100 to both sides
100x/100 = 200,000/100
x = 2,000
This means that before the night of the concert 2,000 seats were bought.
We are still not done with this problem because we want to know how many seats are left the night of the concert. To find this simply subtract 2,000 from the number of original seating (2,500)
2,500 - 2,000 = 500
On the night of the concert there were 500 seats left.
Hope this helped!
~Just a girl in love with Shawn Mendes