An experiment to measure the toxicity of formaldehyde yielded the data in the table below. The values show the percent, [math], of rats surviving an exposure to formaldehyde at a concentration of [math] (in parts per million, ppm) after [math] months.

[math][math][math][math][math][math]
[math]100100100999795
[math]1009998979592
[math]969593908680
[math]969382705836

(a) Estimate [math]:
[math]

(b) Estimate [math]:
[math]

(Be sure that you can give the practical meaning of these two values in terms of formaldehyde toxicity.)

Solution: