A researcher performed an experiment with two groups. She found the difference of the means for each group. Then she combined the groups, chose two new groups, and found the difference between the means of those groups. She repeated this process 200 times. The normal distribution of the difference in the means she found is given below. How great would the difference in means between the first two groups have to be in order to be considered significant?

At least 8
At least 10
At least 9
At least 7

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 0 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)