Calculating when future percentages will occur.

Yesterday we explored percentage of one’s life, and today we will expand on those figures and attempt to figure out when a particular percentage will occur in the future.

We determined that my girlfriend and I have been together for 10.109% of my life. (Today that number changed to 10.119%)

Today’s question: On what date will we hit the 20% mark? 50%?

To start off, we need to figure out our starting point. How many days into my life did the zero mark occur – or better stated, how many days into my life did I meet my girlfriend?

To figure this out, we need to determine how many days are between Sept 23,1980 (my birthday) and March 12, 2005 (the day her and I started dating). In this case it equals 8,932 days.

We need to adjust our standard equation for finding percentages next:

Part P

——— = ——— We now know our percentage, we just need to know the number of days to make this percentage.

Whole 100

D 20(percent)

———— = ——————-

8932 + D 100(percent)

Basically, we are now saying “How many days into the relationship (D) have to pass before that number equals 20% of my entire life (8932 + D)?”

We need to cross multiply:

100D = 20(8932 + D)

Simplify:

100D = 178640 + 20D

Subtract 20D from both sides.

80D = 178640

Divide both sides by 80.

D = 2233

That means 2233 days from the start of my relationship (or 2233+8932 days since I was born), I will be at the 20% mark.

Using this page: http://www.timeanddate.com/date/dateadd.html, we find that 20% will occur on April 23, 2011.

For 50%, we can take a few shortcuts if we think about the question we are asking.

When will I have spent half of my life in this relationship? Restated, that asks when will the days before I met her equal the days after I met her?

So, 8932 days + 8932 days = Number of days at which point 50% occurs (from my birthday.)

8932 + 8932 = 17864 days from my birthday, or Tuesday, August 21, 2029.

See how it works for you!

CD