If for some x R ⁺ 0 , the frequency distribution of the marks obtained by 20 students in a test is, then the mean of the marks is

Step-by-step solution

aligned & Here, f _ i =(x+1)^2+2 x-5+x^2-3 x+x & =2 x^2+2 x-4 & f _ i x_ i =2(x+1)^2+3(2 x-5)+5 (x^2-3 x )+7 x & =7 x^2+2 x-13 aligned aligned & N =20 & f _ i =20 & 2 x^2+2 x-4=20 & x=-4,3 & x=3 aligned [ x R ⁺ 0 ] Now mean aligned ( x ) & = f _ i x_ i ~N & = 7(3)^2+2(3)-13 20 aligned =2.8