a book cost p18 if bought online and p22.50 if bought at the store. the bookstore sold 240 books and took in p4995. how many books were bought online and how many were bought in the store?

Let xxx be the number of books bought online and yyy be the number bought in the store. We are told:

1. Total books:

x+y=240x+y=240x+y=240

2. Total money collected:

18x+22.5y=499518x+22.5y=499518x+22.5y=4995

From the first equation, express yyy in terms of xxx:

y=240−xy=240-xy=240−x

Substitute into the second equation:

18x+22.5(240−x)=499518x+22.5(240-x)=499518x+22.5(240−x)=4995

18x+5400−22.5x=499518x+5400-22.5x=499518x+5400−22.5x=4995

−4.5x+5400=4995-4.5x+5400=4995−4.5x+5400=4995

−4.5x=4995−5400=−405-4.5x=4995-5400=-405−4.5x=4995−5400=−405

x=−405−4.5=90x=\frac{-405}{-4.5}=90x=−4.5−405​=90

Then find yyy:

y=240−90=150y=240-90=150y=240−90=150

So:

• 90 books were bought online.
• 150 books were bought at the store.