设总体 <img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/e928b500d9064333a60768da2b220b5f.png?x-oss-process=image/sharpen,200"/>，如果要求以99.7%的概率保证偏差 <img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/01c40b1f65d04382b4eef6d4b0791191.png?x-oss-process=image/sharpen,200"/> ，问在 <img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/d0305c521b874efe9fe0aabc54e0384e.png?x-oss-process=image/sharpen,200"/>时，样本容量 n 应取多大？（）(已知 <img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/26b3adbbeadc4164af61c0011c4506b7.png?x-oss-process=image/sharpen,200"/>)