A researcher wants to estimate the total number of retired people residing in a certain city. She decides to sample blocks and then sample households within blocks. Four blocks are randomly selected from 300 blocks in the city. The data are given in the following table: Number of households Number of retired residents households sampled per household [Bilengen isl [Bitangan pesere yang meridians sette- a] Identify the sampling unit{s] and state the sampling method used. b] Estimate the average number of retired residents per household. Hence. consthct a 95% condence interval for pr. c] Estimate the total number of retired residents in the city d] Give one advantage of two-stage cluster sampling to one-stage cluster sampling