The standard deviation of 100 observations is 10. If 5 is added to each observation and then divided by 20, then what will be the new standard deviation?

What is the arithmetic mean of 8²,9²,10²,...,15²?

Let x - 3y + 4 = 0 and 2x - 7y + 8 = 0 be two lines of regression computed from some bivariate data. If b_yx and b_xy are regression coefficients of lines of regression of y on x and x on y respectively, then what is the value of b_xy + 7b_yx?

What is the mean deviation of the first 10 natural numbers?