If for some x ∈ R , the frequency distribution of the marks obtained by 20 students in a test is: Marks 2 3 5 7 Frequency distribution x + 1 2 2 x - 5 x 2 - 3 x x Then the mean of the marks is :

Step-by-step solution

Total students = 20 ⇒     x + 1 2 + 2 x - 5 + x 2 - 3 x + x = 20 ⇒       x 2 + 2 x + 1 + 2 x - 5 + x 2 - 3 x + x = 20 ⇒       2 x 2 + 2 x - 24 = 0     ⇒     x 2 + x - 12 = 0 ⇒         x = - 4 ,   3         ∵     x > 0 ∴         x = 3 Average = x + 1 2 × 2 + 2 x - 5 3 + 5 x 2 - 3 x + 7 × x 20 = 32 + 3 + 0 + 21 20 = 2.8 Hence, re