JAMB - Mathematics (1984 - No. 35)
Measurements of the diameters, in centimeters, in centimeters, of 20 copper spheres are distributed as shown below
\(\begin{array}{c|c} \text{Class boundary in cm} & \text{frequency} & \\\hline 3.35 - 3.45 & 3\\ 3.45 - 3.55 & 6\\ 3.55 - 3.65 & 7\\ 3.65 - 3.75 & 4\end{array}\)
What is the mean diameter of the copper spheres?
\(\begin{array}{c|c} \text{Class boundary in cm} & \text{frequency} & \\\hline 3.35 - 3.45 & 3\\ 3.45 - 3.55 & 6\\ 3.55 - 3.65 & 7\\ 3.65 - 3.75 & 4\end{array}\)
What is the mean diameter of the copper spheres?
3.40cm
3.58cm
3.56cm
3.62cm
Explanation
\(\begin{array}{c|c} \text{x(mid point)} & f & fx\\ \hline 3.4 & 3 & 10.2 \\ 3.5 & 6 & 21.0\\3.6 & 7 & 25.2\\3.7 & 4 & 14.8\end{array}\)
\(\sum f\) = 20
\(\sum fx\) = 71.2
mean = \(\frac{\sum fx}{\sum f}\)
= \(\frac{71.2}{20}\)
= 3.56
\(\sum f\) = 20
\(\sum fx\) = 71.2
mean = \(\frac{\sum fx}{\sum f}\)
= \(\frac{71.2}{20}\)
= 3.56
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