In the past you paid $800 per month to rent your apartment. you now pay $900 per month for your rent. what is the percent increase in your rent?

Hello! $800 was the past amount for rent and now it's $900. 900 - 800 is 100. that's a $100 difference. In order to find the percent increase in the rent, we can write and sovle a proportion. It would be set up as change/original = x/100, where change is difference between two numbers and original is the previous price. It would be set up like this:

100/800 = x/100

Let's crossmultiply the values. 100 * 100 is 10,000. 800 * x is 800x. That makes 10,000 = 800x. Now, divide each side by 800 to isolate the x. 800x/800 cancels out. 10,000/800 is 12.5 or 12.5%. Let's check this by multiplying by 112.5%. 800 * 112.5% (1.125) is 900. That's what we're looking for! There. x = 12.5%. The percent increase is 12.5%.