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)
when we move down in yearwise a day decreases. but when a leap year comes 2 days gets decreased..for e.g. 12 jan 2008 --- saturday 12 jan 2007 --- friday 12 jan 2006 --- thursday 12 jan 2005 --- wednesday 12 jan 2004 --- monday.. so in 4 years five days gets reduced... so in this manner we can find out in which year wat day was on 12 jan.. ANSWER ----- it was friday on 12 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)
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