There is a paper called "Analyzing the second derivative to find inflection points" under the "Finding inflection points & analyzing concavity" in the chapter on "Using derivatives to analyze functions." In "Step 1" we follow along to find a second derivative which we all agree is as displayed "20x^2(x+1). In "Step 3" we use this second derivative to test areas between inflection points. One of the test numbers used is "-1/2." The chart there shows f double-prime of "-1/2" as equaling 7.5, but I kept getting the answer 5/2.

I multiplied 20 times (-1/2)^2 to get 20*1/4=5, then I multiplied 5 times (-1/2+1), which I interpreted as +1/2. Therefore I showed 5*1/2 or 5/2 as the result of f double-prime. So I felt the chart should show the answer as 2.5 instead of 7.5.