Q.Explain briefly how a quartile can be located graphically using a 'less than' ogive, without needing to draw the 'more than' ogive as well.

A single 'less than' ogive is enough to read off any partition value, by marking the required cumulative-frequency position on the Y-axis. …

Step 1. Draw the 'less than' ogive — cumulative frequency plotted against the upper boundary of each class, joined by a smooth rising curve.

Step 2. For Q1, mark the point $N/4$ on the cumulative-frequency (Y) axis; for Q3, mark $3N/4$.

Step 3. From that Y-axis point, draw a line parallel to the X-axis until it meets the ogive curve.

Step 4. From the point where this line meets the curve, drop a perpendicular down to the X-axis. The value read off the X-axis at that point is the required quartile. …

Believing that locating a quartile graphically, like the median, requires BOTH ogives to be drawn and their intersection found — the two-ogive-intersection method is specific to the median; any single …