the basic of calender reasoning is described in my slide...hope it would be helpful to all... thank you

1. CONCEPT OF CALENDAR
REASONING.
MADE BY- DHANYA PATEL
SCHOOL- J.N.V. KHEDA

2. INTRODUCTION
Calendar
Year( 1 year)
Months(12 months)
Weeks(52 weeks, 1 odd day)
Days(365 days)

3. WHAT IS LEAP YEAR?
 A year, occurring once every four years, which
has 366 days including 29 February as an
intercalary day.
Calendar
Year( 1 year)
Months(12 months)
Weeks(52 weeks, 2odd day)
Days(366 days)

4. HOW DOES LEAP YEAR FORM?
 As we know that earth rotates sun. Earth takes
365 days (1 year) to finish rotation.
 Approximately earth take 365 days and 6 hrs to
finish 1 whole rotation of sun.
 We do not count this 6 hrs in our ordinary year.
 Once after four year 1 more day is form i.e.
(6+6+6+6)hrs=24 hrs= 1 day.
 So once every fourth year we use to add one in
February.
 This way leap year is form.

5. HOW TO FIND THAT A PARTICULAR YEAR IS
LEAP YEAR ?
 As we know a leap year comes once every fourth
year.
 So to find that the particular year is a leap year
we have to divide the particular year with 4.
 If that year is fully divisible with 4 ,then it is
LEAP YEAR.
 EXAMPLES- Is 2020 a leap year?
=2020/4
= 505
Therefore the obtain result is 505, so the 2020 is
a leap year.

6. HOW TO FIND A LEAP CENTAURY?
 As we know a leap centaury comes once every
fourth year.
 So to find that the particular centaury is a leap
year we have to divide the particular centaury
with 400.
 If that centaury is fully divisible with 400, then it
is LEAP CENTAURY.
 EXAMPLES- Is 1600 a leap centaury ?
=1600/400
= 4
Therefore the obtain result is 4, so the 1600is a
leap centaury .

7. HOW TO COUNT NUMBER OF WEEKS?
Ø 1 year has 365 days.
Ø 1 week has 7 days.
Ø So No. of weeks in a ordinary year
= 365/7
= 52 weeks, 1 odd day
Ø 1 leap year has 366 days.
Ø So No. of weeks in a leap year
=366/7
=52 weeks, 2 odd day

8. HOW TO FIND NO. OF ODD DAYS?
 As we know that an ordinary has 1 odd day &
leap has 2 odd days.
 For example- how many odd days are in 14 years?
 So firstly , we have to find that how many leap
years are there in 14 years.
 So leap years in 14 years= 14/4=2 leap years
 As we know that leap has 2 odd days, so odd days
2 leap years = 2×2=4 odd days
 Now we have to find that how many years are as
simple years
 So by subtracting whole number of years from
leap years we will obtain the No. of simple years

9. HOW TO FIND NO. OF ODD DAYS?
No. of simple years= 14-2
= 12 simple year
As we know that simple year has 1 odd day.
So, No. of odd days in 12 simple year= 12×1
=12 odd days

10. TABLE FOR ODD DAYS
NUMBER OF YEARS NUMBER OF ODD DAYS
100 5
200 3
300 1
400 -
500 4
600 2
700 -
800 -
900 4

11. SHORT TRICK TO REMEMBER
 Let's assume that-
 MONDAY=1
 TUESDAY=2
 WEDNESDAY=3
 THURSDAY=4
 FRIDAY=5
 SATURDAY=6
 SUNDAY=7

12. WHICH DAY WAS ON 1 JANUARY, 2015?
 So firstly we will find odd days.
 For odd days we have to find the no. of leap years and
simple years.
 2000+15
 Here 2000 is leap centaury and leap centaury do not
have any odd days
 Now taking 15 years
 No. of leap year in 15 years=15/4= 3 leap years
 No. of simple year in 15 years= 15-3=12 years
 No. of odd days in 15 years= (12×1)+(3×2)=18 odd days

13. WHICH DAY WAS ON 1 JANUARY, 2015?
 as we know that 1, JAN whole day is over so we
will add it .(18+1=19 odd days)
 19 odd days can be further divided into weeks
 So 18/7=2 weeks and 4 odd days
 So 4 odd days is our final answer
 So the day on 1 JAN , 2015 was THURSDAY
(recap the short trick.)