Here is a fairly simple one for those who are familiar with timetables of the 1970s:
What was common between these four stations as of the mid-70s (but not today):
Answer: These stations had three gauges of lines.
The first to get it right was Abhirup Sarkar.
Notes for those who are interested:
Remember, all this applies to the 1970s and not now.
BG, MG and NG are mentioned in order for each case.
NJP: The main line to New Bongaigaon, branch line from Siliguri, 2’0″ DHR to Darjeeling.
Bangalore City: Main line from Madras, various lines to Mysore, Hubli etc, 2’6″ line to Bangarapet via Yelahanka, Chikballapur and Kolar. The NG terminus moved to Yelahanka in the 80s. Now that line is also BG. Possibly Yelahanka had all 3 gauges for some time.
Miraj: Main line from Bombay and Poona, main line from Bangalore, branch line to Kurduwadi. (Up to around 1970 it was on the MG line from Poona to Bangalore. BG conversion got up to Miraj and Kolhapur and then stopped for many years).
Ujjain: Major branch line from Bhopal to Nagda and Indore, minor branch line from Indore via Fatehabad Chandrawatiganj, 2’0″ branch to Agar which probably closed in the 80s. This was originally part of the Scindia State Railway which also ran three similar branches out of Gwalior, one of which still runs on NG.