A real-life example that uses slope is determining how someone's savings account balance has increased over time. When determining the rate at which the account has increased, the account owner is calculating the slope of the line that shows the changes in the account's balance.
If the account starts out with no money and has $1200 at month 12, the formula to calculate slope is used to show the account's rate of change. The formula reads (y2-y1)/(x2-x1); when the numbers are plugged in, it reads (1200-0)/(12-0), which equals 1200/12. When 1200/12 is simplified, it equals $100. The rate of change for the account is $100 per month, which means this is how much the account owner saves on average each month.