Question:

A child was born on 13th January 1976 which was a Tuesday. What day of the week will be the child’s birthday in the year 1986?

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Same date across years: add $+1$ for each ordinary year and $+2$ for each leap year between them, then reduce modulo $7$.
Updated On: Aug 13, 2025
  • Sunday
  • Friday
  • Saturday
  • Monday
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The Correct Option is D

Solution and Explanation

We move from 13 Jan 1976 to 13 Jan 1986 — a span of 10 years. Each ordinary (non-leap) year advances the weekday by $+1$; each leap year adds $+2$ because of the extra day (Feb 29). Since the date is Jan 13, every leap year in between contributes its extra day.
Years crossed and shifts:
\begin{tabular}{l l} 1976 (leap) & $+2$
1977 & $+1$
1978 & $+1$
1979 & $+1$
1980 (leap) & $+2$
1981 & $+1$
1982 & $+1$
1983 & $+1$
1984 (leap) & $+2$
1985 & $+1$
\end{tabular}
[2mm] Total shift $=2+1+1+1+2+1+1+1+2+1=13$ days.
Take $13 \bmod 7 = 6$. Starting from Tuesday, six days ahead is Monday.
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