Clocks and Calendar - Calendar Problem


 
 
Concept Explanation
 

Clocks and Calendar - Calendar Problem

Calendar Problem: Day of the week repeats itself after every 7 days.

so, if it is a Thursday on 1 Aug, 2013, then it is a Thursday on

1+7times1=8;Aug

1+7times2=15;Aug

1+7times3=22;Aug

1+7times4=29;Aug

Now, we are sometimes confronted by a problem like, if 10 Aug is a Saturday, what day it will be on 27 Aug.

FIrst, let us find the number of days from 10 Aug to 27 Aug.

27- 10 = 17 days. ( 10 Aug not counted )

Now, if we divide 17 by 7, it leaves a remainder of 3.

Now, these 3 days can be called odd days, which are left off after a complete week.

As 10 Aug was a Saturday, the first odd day would be  Sunday, the second Odd day will we Monday

So, the third odd day is Tuesday . Hence, 27 Aug will be a Tuesday.

Illustration: if today is Monday, then after 61 days it will be

A. Wednesday                  B. Tuesday                   C. Saturday                        D. Thursday

Answer: C

Solution:Today is Monday i.e. 1

After 61 days i.e. 5 (Remainder after dividing by 7) would be 1 + 5 = 6 i.e. Saturday

Illustration: On what dates of Aug 1980 did Monday fall?

A. 4th,11th,18th and 25th                  B. 3rd,10th,17th and 24th                  C. 6th,13th,20th and 27th                     D. 9th,16th,23rd and 30th

Answer: A

Solution:  Take the date as 1st August 1980

We will consider an year previous to the current year. As current year is 1980 we will take year 1979

Nearest Century year when the number of odd days is zero is 1600

Remaining years = 1979 - 1600 = 379

We know that odd days in 300 years = 1

Remaining years = 79

Odd days in 79 Years = 19 Leap Year + 60 Normal Years

                                       = 19 x 2 odd days + 60 x 1 odd day

                                       = 38 + 60 odd days = 98 odd days = 0 odd day (remainder after dividing 98 by7)

Thus on 31.12.1979 = 1 + 0 = 1 i.e. Monday

Now, in 1980, take odd days of each month upto date i.e. Jan - 3, Feb - 1, Mar - 3, Apr - 2, May - 3, Jun - 2, Jul - 3, Aug - 1 = 18 i.e. 4 (Remainder after dividing 18 by 7)

Thus, on 1st August 1980 = 1 + 4 = 5  i.e.Friday

Thus, Monday would be on 4th, 11th, 18th and 25th

Hence the correct option is A

Sample Questions
(More Questions for each concept available in Login)
Question : 1

Today is Thursday. The day after 59 days will be

Right Option : A
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Explanation
Question : 2

Which year next to 1990 will have the same calendar as that of the year 1990?

Right Option : C
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Explanation
Question : 3

If 5th February was Sunday, how many Monday there in that month ?

Right Option : B
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Explanation
 
 


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