for every 500 minutes, the number of bacteria in a petri dish decreases by 20. Which rational number shows the average change in bacteria?

Compare the subtraction problems 6/8 - 5/8 = 1/8 and 6/9 - 7/9 = 1/9 why is the answer to the first problem positive and the answer to the second problem negative

Me because some of question i don’t understand

Combine the information in the problem and the chart using the average balance method to solve the problem.