Birthday Math

Number Theory Level pending

Five siblings wrote down their birth dates and the corresponding day:

  • Charles: 24 Sept 1991 (Friday)

  • Darius: 30 May 1994 (Thursday)

  • Brenda: 19 Nov 1996 (Wednesday)

  • Alfred: 1 Nov 1999 (Tuesday)

  • Eric: 4 Dec 2000 (Monday)

One of them identified the day correctly. Given that 1 Jan 2015 falls on a Thursday, who is correct?

Darius Alfred Charles Brenda Eric

Noel Lo by Noel Lo , 24, Singapore

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Yosua Sibuea
Oct 17, 2015
  1. September 24th 1991 (Tuesday)
  2. May 30th 1994 (Monday)
  3. November 19th 1996 (Tuesday)
  4. November 1st 1999 (Monday)
  5. December 4th 2000 (Monday)

So, the correct one is Eric.

3 Helpful 0 Interesting 0 Brilliant 0 Confused
Henny Lim
Oct 22, 2015

Use the facts that: 1. All twin even dates (Apr 4, Jun 6, Aug 8, Oct 10, and Dec 12, and Feb 2 also in the non-leap year, or Feb 1 in the leap year) always fall on the same day. 2. We can get "what day was Jan 1" based on given day of Jan 1, 2015; by substracting the day: By 1 day in the non-leap year, or by 2 days in the leap year.

By calculating with the nearest date with given dates, we can easily determine that Eric was correct.

2 Helpful 0 Interesting 0 Brilliant 0 Confused

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...