### Home > CCA2 > Chapter 11 > Lesson 11.1.1 > Problem11-8

11-8.

Eeeeew! Hannah’s volleyball teammates left their egg salad sandwiches sitting in their lockers over the weekend. When they got back on Monday, the sandwiches were moldy. “Perfect!” said Hannah. “I can use these sandwiches for my biology project. I’ll study how quickly mold grows.”

Using a transparent grid, Hannah estimated that about $12\%$ of the surface of one sandwich had mold on it. She threw the sandwich out. For the rest of the week, Hannah came back when she had time. Each time she measured somebody else’s sandwich and threw it out. She collected the following data:

 Day $1$ (Monday) Day $2$ (Tuesday) Day $2$ (Tuesday) Day $4$ (Thursday) Day $4$ (Thursday) Day $4$ (Thursday) Day $5$ (Friday) $12\%$ $15\%$ $13\%$ $26\%$ $27\%$ $24\%$ $38\%$

1. Create a scatterplot and sketch it. Is a linear model reasonable?

Your graph should show that the data looks 'curved'.

2. Based on the story, what kind of equation do you think will best fit the situation?

What types of models are curved?

3. Fit an exponential model to the data and write the equation. What percentage of a sandwich did Hannah predict was covered on Wednesday? Consider the precision of Hannah’s measurements when deciding how many decimal places to use in your answer.

Enter the data into your calculator then calculate the exponential regression.