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Measurements of the diameters, in centimeters, of 20 copp...

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

A.

3.40cm

B.

3.58cm

C.

3.56cm

D.

3.62cm

Correct answer is C

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

\(\sum f\) = 20

\(\sum fx\) = 71.2

mean = \(\frac{\sum fx}{\sum f}\)

= \(\frac{71.2}{20}\)

= 3.56