Nasir's birthday in a certain year falls on Thursday, 18th May. In the same year, Rehan was born on 19th August. On which day of the week does Rehan's birthday fall in that year?

Introduction / Context:
This is another calendar problem relating two birthdays in the same year. You are told the weekday for Nasir's birthday and asked to find the weekday for Rehan's birthday. The two dates are separated by several months, so you must count the days between them carefully and then translate that total into a weekday shift using modulo arithmetic.

Given Data / Assumptions:

• Nasir's birthday: Thursday, 18th May.
• Rehan's birthday: 19th August of the same year.
• Standard month lengths:
  • May: 31 days
  • June: 30 days
  • July: 31 days
  • August: 31 days
• Leap year vs non-leap year does not affect this calculation because all relevant dates are after February.

Concept / Approach:
First, we count the number of days from 18th May to 19th August. Then we take the total modulo 7 to find how many days ahead we move from Thursday. This gives the weekday of Rehan's birthday.

Step-by-Step Solution:
Step 1: Days remaining in May after 18th May: 31 - 18 = 13 days (19th to 31st). Step 2: Full months between June and July: June: 30 days, July: 31 days. Step 3: Total days for June and July = 30 + 31 = 61 days. Step 4: Days in August up to 19th August = 19 days. Step 5: Total days between 18th May and 19th August = 13 (May) + 61 (June and July) + 19 (August) = 93 days. Step 6: Compute 93 mod 7. Since 7 * 13 = 91, remainder is 93 - 91 = 2. Step 7: A remainder of 2 means the weekday moves forward by 2 days from Thursday. Step 8: Starting at Thursday: Friday (1), Saturday (2). Step 9: Therefore, Rehan's birthday on 19th August falls on a Saturday.

Verification / Alternative check:
Think of the 93-day difference as 13 full weeks (13 * 7 = 91 days) and 2 extra days. Thirteen full weeks return us to Thursday, and the 2 extra days land us on Saturday. Because the dates are after February and month lengths are standard, this result is stable regardless of the specific year.

Why Other Options Are Wrong:
Wednesday would correspond to a backward shift, Friday to only a 1-day shift, Thursday to 0 shift, and Sunday to a 3-day shift from Thursday. None of these match the 2-day shift indicated by 93 days, so they cannot represent the correct weekday for Rehan's birthday.

Common Pitfalls:
It is easy to miscalculate days left in the starting month or to misremember that June has 30 days while July and August have 31. Writing down each month and its days helps avoid these errors. Also, some students try to step through every day instead of using modulo arithmetic, which is slower and more error-prone.

Final Answer:
Rehan's birthday in that year falls on Saturday.