If for some positive x I R , the frequency distribution of the marks obtained by 20 students in a certain test, is as follows Then the mean of the marks is

Step-by-step solution

Here, total number of students =20 aligned & (x+1)^2+(2 x-5)+ (x^2-3 x )+x=20 & 2 x^2+2 x-4=20 & x^2+x-12=0 & (x+4)(x-3)=0 & But x=3[ as x>0] aligned Now required mean = aligned & 2 (3+1)^2+3 (2 3-5)+5 (3^2-3 3 )+7 3 20 & = 2 16+3 1+5 0+7 3 20 & =2.8 aligned