Can you find out what day of the week was January 12, 1979?

Ans. Friday.

• 12th Jan 1979
  
  1979 = 1900yrs + 78yrs + (period from 1st Jan to 12th Jan 1979)
  1900 yrs have 1 odd day(calculated as 1600yrs have 0 odd days, n 300yrs have 15 odd days i.e.15/7= 2 weeks+1 odd day.so,for 300yrs, it's 1 odd day.totally it's 0+1=1odd day for 1900yrs).
  78yrs = 19leap yrs +59 ordinary yrs
  = 19 *2 +59 *1
  = 97days = 13weeks +6 odd days = 6 odd days
  period from 1st Jan to 12th Jan 1979 =12 days = 1week + 5odd days = 5 odd days
  Therefore,
  12th Jan 1979 = 1+6+5 = 12days =1 week +5 odd days =5 odd days
  Therefore, 12th Jan 1979 was a Friday.
  (Since,Sunday->0,Monday->1,...,Fri->5,sat->6)
• 12 years agoHelpfull: Yes(7) No(6)
• January code=0 since date below 1999 so take last 2 digit i.e., 79/4 and keep quotiient=19
  mention day=12
  Result=79+19+0+12=110
  divide result by 7 we get 5 is reminder Hence Friday is Answer
• 8 years agoHelpfull: Yes(2) No(3)
• 1979years=1900 years+78 years+1 jan to 12 jan
  1900=1600(0 odd days)+300(1 odd day)==1 odd day
  78 years contains 78/4=19 leap years and 59 ordinary years
  19 leap years=19*2=38 odd days
  59 ordinary years=59 odd days
  38+59+1=98odd days
  98/7=0 odd days
  so,till 31 dec 1978 there are 0 odd days
  
  lets talk about now 12 jan contains==5 odd days
  therefore as 5=friday
  so,12 jan 1979 was friday
• 7 years agoHelpfull: Yes(0) No(0)
• As 12th January 1979 = 1900 years + 78 years + period from 1st Jan. to 12 Jan. 1979
  
  So No. of odd days in 1600 years = 0
  
  No. of odd days in 300 years (1900 – 1600) = (5 × 3) ÷ 7 = 2 weeks + 1 odd day
  
  No. of odd days in 78 years = 19 leap year + 59 ordinary years
  
  = {(19 × 2) + (59 × 1)} ÷ 7= (38 + 59) ÷ 7 = 97 ÷ 7 =13 weeks + 6 odd days
  
  No. of odd days in period from 1st Jan. to 12 Jan. 1979 = 12 days = 12 ÷ 7 = 1 week + 5 odd days
  
  Total odd days = 1 + 6 + 5 = 12 days = 12 ÷ 7 = 1 week + 5 odd days
  
  So 12th January 1979 is Friday as Sunday is 0; Monday is 1 and so on.
  Note:
  1) A leap year is a year which is divisible by 4.
  2) No. of odd days in a leap year is 2 and in an ordinary year is 1
  3) No. of odd days in every 100 years is 5 and each multiple of 400 is 0.
• 6 years agoHelpfull: Yes(0) No(0)