估算.
503×7≈
590×6≈
825×4≈
512×7≈
(1)503×7≈3500;
(2)590×6≈3600;
(3)825×4≈3200;
(4)512×7≈3500.
胃气钡双重造影时,显示胃小区大小为直径约()
A.0.5~1mm
B.0.5~2mm
C.1~3mm
D.2~4mm
E.3~5mm
An analyst does research about sampling. Compared to estimates of parameters produced from simple random sampling, estimates of parameters produced from stratified random sampling most likely have:
A. less precision.B. the same precision.C. greater precision.