Theo dõi phát triển dân số xã X thu được số liệu sau: Z năm X (số dân, người) Y (tỷ lệ chết, đv: 1)
2016 4.670 0,0099
2017 4.860 0,0074
2018 5.050 0,0099
2019 5.170 0,0064
2020 5.470 0,0059

a) Tính hệ số tương quan rxy và cho nhận xét ?
b) Hỏi năm 2021 dân số xã X là bao nhiêu

Exercise: counting committees 0.0/2.0 puntos (calificable) we start with a pool of n people. a chaired committee consists of k≥1 members, out of whom one member is designated as the chairperson. the expression k(nk) can be interpreted as the number of possible chaired committees with k members. this is because we have (nk) choices for the k members, and once the members are chosen, there are then k choices for the chairperson. thus, c=∑k=1nk(nk) is the total number of possible chaired committees of any size. find the value of c (as a function of n ) by thinking about a different way of forming a chaired committee: first choose the chairperson, then choose the other members of the committee. the answer is of the form c=(α+nβ)2γn+δ. what are the values of α , β , γ , and δ ?