a construction engineer is faced with the problem of assessing the tile damage in a certain group of downtown buildings. the total number of tiles on these buildings is around five million (too large) and it is far too costly to examine each tile in detail for cracks. therefore the engineer constructs a sample of 1250 tiles chosen randomly from the blueprints of the building and examines each tile in the sample for cracking. the engineer is interested in the true overall proportion of all the tiles that are cracked. out of the sample of tiles, are found to be cracked. (a) calculate a 90% confidence interval for the true proportion of cracked tiles. lower bound [ select ] upper bound [ select ] (b) now, suppose that the engineer wants to calculate a 95% confidence interval for the true proportion of cracked tiles that has margin of error equal to 0.07. how many tiles will she have to sample to achieve this? [ select ]