What Day of the Week was 4/13/96?

Date: 07/12/2002 at 23:21:17
From: Phyllis Zane
Subject: Finding the day of the week 6 years ago.

I am trying to prepare my grand-daughter for a city-wide 5th grade 
math test. We have some of the previous tests and this is one of the 
questions I cannot solve. I have checked out 31 math books from 
the nearest libraries and they have been helpful for most of the
questions, but there is nothing on this problem:

What day of the week was April 13, 1996? I know the answer is 
Saturday but I have no idea how to find the answer.

Thank you for any help you can give me.  

Phyllis

Date: 07/13/2002 at 17:55:53
From: Doctor Ian
Subject: Re: Finding the day of the week 6 years ago.I

Hi Phyllis,

I assume you want to figure it out without just looking it up on 
a calendar, right? 

From 4/13/96 to 4/13/97 is 365 days; to 4/13/98 is another 365 
days; and so on, up to 4/13/02.  That's 6*365 days in total.  
Since 2000 was a leap year, you have to add an extra day.  So 
we have (6*365+1) days from 4/13/96 to 4/13/02. 

That's a total of 2191 days, which turns out to be exactly 313 
weeks.  So whatever day 4/13/96 was, 4/13/02 is the same day.

And you can figure out what day 4/13/02 must have been by 
counting weeks forward until today:  

  4/13, 4/20, 4/27, 
  5/4,  5/11, 5/18, 5/25, 
  6/1,  6/8,  6/15, 6/22, 6/29,
  7/6,  7/13

Today is 7/13, and it's Saturday; so 4/13/02 must have been a 
Saturday too; which means that 4/13/96 must have been one as well.

If you were answering the question on some other day, you'd have 
to stop counting weeks at some point, and count days instead.  

Does this help? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/