Question: The price of a commodity in a store on day 'k' is a RV \[{{X}_{k}}\]and satisfies \[{{X}_{k}}={{X}_{k-1}}+{{U}_{k}}\], where \[E\left( {{U}_{k}} \right)=0,\,\,\operatorname{var}\left( {{U}_{k}} \right)=4\], where \[{{U}_{k}}\]is the price increase on day 'k'. Assume that \[{{U}_{1}},{{U}_{2}},...\] are independent and the price of commodity is 50 today. Calculate the probability that the price 25 days later will be between 47 and 53.