90) The income of a group of 10000 persons were found to be normally distribution with mean Rs.500.00 and standard deviation Rs.60. Find the number of persons having incomes between Rs.400 and Rs.500. (For a standard normal variate t , the area under the curve between t=0 and t=0.5 is 0.19146, the area between t=0 and t=1.645 is 0.45000 and the area between t=0 and t=2 is 0.47725, Area between t=0 and t=1.67 is 0.4525.)