In a normally distributed group of 15,000 students with a mean score of 60 and a standard deviation of 10, approximately how many students scored between 50 and 70 marks?

In a normal distribution, approximately what proportion of values falls within one standard deviation (±1σ) of the mean?

In a normally distributed group of 15,000 students with a mean score of 60 and a standard deviation of 10, find the difference between the number of students scoring between 40-80 and those scoring between 50-70.