materials of construction course question

Table 1 is a collection of testing records of concrete cylinders 150300mm compressive strength tests for construction of a shopping center. (a) Determine the mean, standard deviation and characteristic strength of the concrete at 2.5% defective level. (b) Draw a histogram (frequency distribution) of the compressive strength test results in Table 1 (frequency: 2MPa ). (c) Draw the normal distribution (Gaussian) curve based on the compressive strength test results in Table 1. Table 1: Compressive strength test results of specimens at 28-day