The mean midday temperature recorded in June in a city in South California is 36ºC, and the standard deviation is 3ºC. The number of days in the month of June is 30. Assuming the data is normally distributed, the number of days in June when the midday temperature was between 39ºC and 42ºC is .

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 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)