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Continuous series means where frequencies are given along with the value of the variable in the form of class intervals. For example.

**Here:**

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(i) 10-20, 20-30 … etc. are class intervals.

(ii) 3, 7, 11, 9, 6 is known as their respective frequencies.

(iii) In 20-30, 30-40…. etc. 20 is the lower and 30 the upper limit of 20-30 class interval.

(iv) Adding both the limits and taking their average, we get midpoint of the class interval. The mid-value of 20-30 is ; 20+30/2 = 25.

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It is often denoted by m or X.

When we take mid points of class Intervals, it can be denoted by *X*, *m* or *M* X can be found by three methods.

**Other Special Cases of Continuous Series****: **

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Series such as in the last example i.e. 10—20, 20—30, 30—40……….. is known as Exclusive Series.

For other types of continuous series as discussed below, all the series are first converted into exclusive series and then preceded for the solution as above.

Important: It is regarded essential to convert all other types of series into exclusive type ; Otherwise we will proceed to a wrong result.