If 1$$^{st}$$ January 2017 was a Thursday, then what day of the week was it on 31$$^{st}$$​ March of that year?

1st Jan 2017 → Thursday (as per the question)

We now calculate the number of days between 1st Jan and 31st March:

January: 31 days → Remaining = 30 days (excluding 1st Jan)

February: 28 days (2017 is not a leap year)

March: 31 days

Total = 30 (Jan) + 28 (Feb) + 31 (Mar) = 89 days

Now divide 89 by 7 to get how many weeks and extra days:

89 ÷ 7 = 12 weeks and 5 days

So,

If 1st Jan is Thursday,

then:31st March will be Thursday + 5 days = Tuesday