Measurements of the diameters, in centimeters, in centimeters, of 20 copper spheres are distributed as…

Measurements of the diameters, in centimeters, in centimeters, of 20 copper spheres are distributed as shown below
(begin{array}{c|c} text{Class boundary in cm} & text{frequency} & \hline 3.35 – 3.45 & 3\ 3.45 – 3.55 & 6\ 3.55 – 3.65 & 7\ 3.65 – 3.75 & 4end{array})
What is the mean diameter of the copper spheres?

Correct Answer: Option C

Explanation

(begin{array}{c|c} text{x(mid point)} & f & fx\ hline 3.4 & 3 & 10.2 \ 3.5 & 6 & 21.0\3.6 & 7 & 25.2\3.7 & 4 & 14.8end{array})
(sum f) = 20
(sum fx) = 71.2
mean = (frac{sum fx}{sum f})
= (frac{71.2}{20})
= 3.56