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Based on past experience, it is known that standard deviation of weight of one year old rohu fish is 25 g. If it is decided to
estimate mean weight within 5 units of true value in either direction with confidence coefficient of 0.95 (note that the standard
normal variate Z takes the value 1.96 ~ 2 approximately, at this 95% confidence level), then if the sampling is done with
SRSWR and that the finite population correction is ignored, the required sample size is approximately