Two students are inviting friends to a mutual party, each student is inviting 5 of their 15 mutual friends, what is the probability that they will invite the same 5 friends?
A. 1 in 360360
B. 1 in 3003
C. 1 in 4368
D. 1 in 8008
( please help :( this is a question from Plato )

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)