In a non-leap year, if the first day of the year was Monday, then which day of the week was the last day of that year?

Introduction / Context:
In calendar based reasoning questions, exams often test whether you understand how days of the week repeat over fixed intervals. A non leap year has 365 days, which is not exactly a multiple of seven, so the starting and ending days of the year are closely related. This question asks you to connect the first day of a non leap year with its last day using simple modular arithmetic on days of the week.

Given Data / Assumptions:
- The year under consideration is explicitly stated to be a non leap year. - A non leap year has 365 days. - The first day of this year is Monday. - The week cycle repeats every 7 days.

Concept / Approach:
The key concept is that days of the week repeat after every block of seven days. If the total number of days in a period is of the form 7k, the starting and ending days are the same. For a non leap year with 365 days, we look at 365 in terms of complete weeks plus the remainder. Once we know how many extra days are left beyond full weeks, we shift the first day forward by that remainder to get the last day of the year.

Step-by-Step Solution:
Step 1: Note that a non leap year has 365 days. Step 2: Express 365 as full weeks plus remainder: 365 = 52 * 7 + 1. Step 3: The term 52 * 7 represents 52 complete weeks, which do not change the day of the week pattern. Step 4: The remainder is 1 day, which means the last day of the year is exactly one weekday step ahead of the first day. Step 5: If the first day is Monday, shifting forward by 1 normally gives Tuesday. However, here we must be careful about counting positions of days. Step 6: Day 1 of the year is Monday. Day 8 is also Monday, and so on. Day 365 is 364 days after day 1, which is 52 full weeks (364 days). Therefore the 365th day falls on the same weekday as the first day. Step 7: Hence the last day of the year is again Monday.

Verification / Alternative check:
One quick verification is to consider the simple idea that 364 is exactly 52 * 7. If you start from Monday and move forward by 364 days, you complete 52 full weeks and land on Monday again. Day 1 is Monday, day 365 is 364 days later, so day 365 is also Monday. This confirms that the first and last days of a non leap year are the same weekday. Therefore the answer Monday is fully consistent with the arithmetic of weeks and days.

Why Other Options Are Wrong:
Friday: This would be correct only if the remainder created a shift of four days, which is not the case here. Saturday: This would correspond to a remainder of five days between first and last day, which does not match 365 days. Sunday: This would be appropriate if the effective shift produced a six day difference, which again does not match the calculation.

Common Pitfalls:
Many learners mistakenly assume that because 365 divided by 7 leaves a remainder of 1, the last day must be one day ahead of the first, and they forget to relate the remainder to the position of the last day. The correct way is to compare day 1 and day 365 by looking at the difference of 364 days, not 365. Another common confusion is mixing up leap years and non leap years, which changes the total days and the remainder. Being precise about which day is counted as day 1 avoids these errors.

Final Answer:
Thus, in a non leap year where the first day is Monday, the last day of the year is also Monday.