Q.Explain how the median of a continuous series can be found graphically using ogives.

The two ogives of a distribution, drawn on the same axes, intersect at a single point that directly gives the median.

Step 1. Construct the 'less than' ogive by plotting the cumulative frequency (the number of observations up to each class) against the upper class boundary of every class, and joining the points with a smooth curve — this curve is always rising.

Step 2. Construct the 'more than' ogive by plotting the cumulative frequency (the number of observations at or above each class) against the lower class boundary of every class — this curve is always falling.

Step 3. Draw both ogives on the same pair of axes, using the same scale. The two curves intersect at exactly one point.

Step 4. Drop a perpendicular from this point of intersection down to the X-axis; the value read off the X-axis at that point IS the median of the distribution. …

Plotting the 'less than' ogive against the LOWER class boundary (or the 'more than' ogive against the UPPER class boundary) reverses the intended construction and shift …