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Exercises · Q15

Q.In the mode formula for a continuous series, Mode=L+f1−f02f1−f0−f2×hMode = L + \dfrac{f_1-f_0}{2f_1-f_0-f_2}\times h, what does f1f_1 represent?

(a) The frequency of the class preceding the modal class
(b) The frequency of the modal class
(c) The frequency of the class succeeding the modal class
(d) The total frequency of the distribution
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Correct option: (b) The frequency of the modal class.

In the interpolation formula Mode=L+f1−f02f1−f0−f2×hMode = L + \dfrac{f_1-f_0}{2f_1-f_0-f_2}\times h:

  • LL = lower limit of the modal class.
  • f1f_1 = frequency of the modal class itself — the highest frequency in the whole distribution.
  • f0f_0 = frequency of the class immediately preceding the modal class.
  • f2f_2 = frequency of the class immediately succeeding the modal class.
  • hh = width of the modal class.

Using Worked Example 10's data (modal class 30–40 with frequency 16, preceding class 20–30 with frequency 15, succeeding class 40–50 with frequency 6): here f1=16f_1 = 16 is exactly the highest frequency in the table, confirming that f1f_1 denotes the modal class's own frequency, not any neighbouring class.

Why the other options are wrong:

  • (a) describes f0f_0, not f1f_1 — the preceding class's frequency is subtracted in the numerator and denominator, but it is not what f1f_1 stands for. …

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