Starting from 20 January 2017, which is given as a Sunday, what will be the exact calendar date and day of the week after 90 days from that day?

Introduction / Context:
This question tests your understanding of how to move forward through the calendar by a fixed number of days, and how to track both the date and the day of the week. Problems that say something like “today is” followed by a specific date and weekday are very common in calendar aptitude topics and help build confidence with date arithmetic.

Given Data / Assumptions:

• Today is 20 January 2017.
• The day on 20 January 2017 is stated to be Sunday.
• We need to find the date and weekday that is exactly 90 days after this given day.
• Months have their usual lengths: January 31 days, February 28 days in a non leap year, and March 31 days.
• We treat 2017 as a non leap year since February 2017 has 28 days.

Concept / Approach:
The approach is to calculate how many days remain in January after the twentieth, then add full months, and finally add any remaining days to reach a total of 90. In parallel, we use the fact that every block of 7 days brings us back to the same weekday, so we only need the remainder when 90 is divided by 7 to shift the weekday correctly from the starting Sunday.

Step-by-Step Solution:
Step 1: Remaining days in January after 20 January are 31 minus 20 = 11 days. Step 2: Days in February 2017 are 28 days, and days in March are 31 days. Step 3: Add these to get 11 + 28 + 31 = 70 days from 21 January to 31 March inclusive of 31 March. Step 4: We need 90 days total, so remaining days after 31 March are 90 − 70 = 20 days. Step 5: Counting 20 more days into April leads us to 20 April as the target date. Step 6: To find the weekday, note that 90 divided by 7 gives a remainder of 6, so the day moves forward by 6 days from Sunday. Step 7: Starting at Sunday and moving forward 6 days gives Saturday as the weekday on 20 April.

Verification / Alternative check:
You can also group 90 days as 84 days plus 6 days. Exactly 84 days correspond to 12 full weeks, so they cycle the weekday back to Sunday. Then only the extra 6 days matter. Moving 6 days ahead from Sunday goes to Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, which again confirms that the weekday is Saturday. This double check supports our calculation of both the date and the day.

Why Other Options Are Wrong:
18 April, Friday is two days earlier than the correct date and also one weekday off. 21 April, Sunday is one day ahead of the correct date and does not match the weekday shift. 19 April, Saturday is one date too early compared to the proper count of 90 days. Only 20 April, Saturday matches both the number of days and the weekday shift from the starting Sunday.

Common Pitfalls:
A common mistake is to forget whether to include or exclude the starting day when counting. In standard aptitude questions, when we say “90 days from today” we usually count the days after the current day, not including it. Another error is miscounting the days in February or March, which can shift the result by one or more days. Finally, when handling weekdays, some candidates incorrectly add full multiples of 7 to the remainder, which is unnecessary since multiples of 7 do not change the weekday.

Final Answer:
Therefore, 90 days from 20 January 2017, given as a Sunday, falls on 20th April, Saturday.