Gurkiran's birthday in a particular year falls on Sunday, 21st May. In the same year, Shreyas was born on 14th November. On which day of the week does Shreyas's birthday fall in that year?

Introduction / Context:
This calendar aptitude question links two birthdays within the same year. You are given the weekday for Gurkiran's birthday and asked to find the weekday for Shreyas's birthday. The challenge lies in counting the days between the two dates across several months and then translating that total into a shift in weekdays.

Given Data / Assumptions:

• Gurkiran's birthday: Sunday, 21st May (in a certain year).
• Shreyas's birthday: 14th November of the same year.
• Month lengths (non-leap year, but leap vs non-leap does not affect relative difference here since both dates are after February):
  • May: 31 days
  • June: 30 days
  • July: 31 days
  • August: 31 days
  • September: 30 days
  • October: 31 days
  • November: 30 days

Concept / Approach:
We must count the total number of days between 21st May and 14th November. Then we reduce this total modulo 7 to see how many days forward we move from Sunday. Because both birthdays fall after February, whether the year is leap or not does not change the day difference between these two particular dates.

Step-by-Step Solution:
Step 1: Days remaining in May after 21st May: 31 - 21 = 10 days (22nd to 31st). Step 2: Full months between June and October: June: 30 days, July: 31 days, August: 31 days, September: 30 days, October: 31 days. Step 3: Sum of these full months: 30 + 31 + 31 + 30 + 31 = 153 days. Step 4: Days in November up to 14th November: 14 days. Step 5: Total days between 21st May and 14th November = 10 (May) + 153 (June to October) + 14 (November) = 177 days. Step 6: Compute 177 mod 7. Since 7 * 25 = 175, we have 177 - 175 = 2, so remainder is 2. Step 7: A remainder of 2 means we move 2 days forward from Sunday. Step 8: Sunday + 1 day = Monday; Monday + 1 day = Tuesday. So Shreyas's birthday is on Tuesday.

Verification / Alternative check:
Thinking in terms of whole weeks, 177 days correspond to 25 full weeks (175 days) plus 2 extra days. Every full week brings us back to the same weekday, so only the 2 extra days influence the final weekday. Starting from Sunday and moving 2 days ahead again lands on Tuesday. This matches our earlier calculation and confirms the answer.

Why Other Options Are Wrong:
Wednesday would require a shift of 3 days from Sunday, Friday a shift of 5 days and Saturday a shift of 6 days. Monday would require only a 1-day shift. None of these correspond to the exact 2-day shift that results from 177 days between the birthdays, so they are all incorrect.

Common Pitfalls:
It is easy to miscount the days in each month or forget one of the month boundaries. A systematic approach—first completing the current month, then adding full months, then adding days in the final month—greatly reduces errors. Always remember to apply modulo 7 to convert day counts into weekday shifts.

Final Answer:
Shreyas's birthday in that year falls on Tuesday.