Question 4 [15 marks] One commercial decision aimed at keeping production costs low in the development of thermal energy storage batteries is to use sand as the storage medium. This is an attractive choice since there are additional sustainability considerations if waste sand from the mining industry is used, for example. However, knowledge of the thermal properties of the sand used in the battery is needed in order to design optimal operating conditions, such as minimum and maximum temperatures, charging duration, storage period for maximum efficiency. Hence, taking measurements of material properties such as the thermal conductivity k (WK-m-1) is essential. Table 2 lists measurements of thermal conductivity, taken at 25 C, for two different sand types. The sand is not homogeneous, therefore in order to have a better measurement, 4 samples are taken for each type. Perform appropriate statistical testing to determine if the thermal conductivity of the two sand types is statistically different. Note that as part of your answer you should choose an appropriate level of significance for your test. Table 2. Thermal conductivity data. Thermal conductivity (WKm) Sample 1 51234 0.253 0.256 0.256 0.257 0.237 0.239 0.239 0.236 Type 2