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Calendar — Concept, Formulas & Examples

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Free LRDI notes on Calendar for CAT-MBA — learn the concept, then practise.

 

INTRODUCTION

Questions from the topic 'Calendars' are frequently asked in exams like NMAT & SNAP. You would not see Calendar questions in CAT, though its concepts may be required to solve some questions.

 

ODD DAYS

A variety of questions in Calendars is that you would be given a day of the week for a reference date and you would be asked to calculate day of the week of a future/past date.

We know, that a week comprises of 7 days. So, day of the week will repeat after every 7 days. To calculate day of the week for a future/past date, we calculate the number of odd days between two dates and then calculate the day of the week accordingly. Let us understand this with an example.


Example
If 1st January was Monday, what day of the week will it be on 28th February of the same year?

Solution:
We first calculate the number of days after 1st January till 28th February.

1st of January is already done, so, January has 30 more days and February will have 28 days till 28th February. Hence, total 30 + 28 = 58 days.

Now, 7 days make a week, hence there will be [Quotient of 58/7 =] 8 complete weeks between these two days.

Day of the week repeats every week, hence at the end of these 8 weeks, day of the week will be Monday.

Apart from these complete weeks, there will be [Remainder of 58/7 =] 2 days remaining which not form a complet week. These are called 'ODD DAYS' and this is what we are interested in.

Day of the week after these 2 days will be Monday + 2 days = Wednesday.

∴ Once we calculate the odd days, day of the week can be calculated.


Example
If 21st March was Sunday, what day of the week will it be on 5th August of the same year?

Solution:
We first calculate the number of days after 21st March till 5th August.

21st of March is already done, so, March has 10 more days
April has 30 days
May has 31 days
June has 30 days
July has 31 days
August has 5 more days.
Hence, total days = 10 + 30 + 31 + 30 + 31 + 5 = 137 days.

Now, number of odd days = Remainder of 137/7 = 4 days.

Day of the week after these 4 days will be Sunday + 4 days = Thursday.

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