If for some x∈R, the frequency distribution of the marks obtained by 20 students in a test is (with cell frequencies expressed in terms of x), then the mean of the marks is:
Solutions · 1
Official solution
Number of students: (x+1)2+(2x−5)+(x2−3x)+x=20
\[2x^2+2x-4=20 \implies x^2+x-12=0 \implies (x+4)(x-3)=0 \implies x=3\]
\[\text{Average marks} = \frac{32+3+21}{20} = \frac{56}{20}=2.8\]