Question

if mean is 39.71 find x

Answer 1

first we need to find mid value of each class interval hence 20,30,40,50,60,70,80 are respective mid values now multiply them by their class Intervals respective frequencies so 120+330+40x+200+240+140+80=> 1110+40x is the total sum . The total all of frequencies is 6+11+X+4+4+2+1 => 28+x. Mean =39.71
=> 278/7 = 1110+40x/28+x => 278(28)+ 278x= 280x+
7770 => 7784-7770 = 2x => x=7.