Change Management

During a consulting interview, it is likely that a potential candidate will be given a brain teaser in order to assess the individual's ability to logically work through a problem.

With this in mind, I thought I'd attempt to unearth one of the most intriguing questions of all time and perhaps the greatest brain teaser ever given to a potential consultant candidate.

Some brain teasers include: Why are manhole covers round?, How many pennies would it take to reach the top of the Empire State Building?, How many golf balls fit into a Boeing 747? (Vault.com)

As you can see, the questions are quite abstract and probably would tell an interviewer a great deal about how that applicant works through ambiguous problems. But, after a while, these same brain teasers can become boring. Therefore, I wanted to work through my very own brain teaser that I find particularly interesting.

• How much time does the average person engage in sexual intercourse during their lifetime?

In order to answer this question we have to consider many things, but it will be necessary to break down one's lifespan into sizable chunks that can be dealt with in a logical way, due to the fact that people are engaging in more or less sexual activity depending on their age on average.

First, some background information. I am only going to figure this out for the United States population. Other countries may be having more or less sexual intercourse over a lifetime. The average lifespan for an individual living in the United States is 78.06 years according to Wikipedia. This ranks as tied for 30th place in the whole world. The life expectancy is slightly different for males and females, but for purposes of this brain teaser, we will just take the average age.

Now we have to consider when people actually start having sexual intercourse. According to a publication by American Sexual Behavior, an individual's first sexual experience will occur around the age of 17 years. I will then assume that once an individual starts having sexual intercourse they will be able to continue to do so. Therefore, there are 61.06 years of life in which sexual intercourse is possible on average.

However, the frequencies of sexual intercourse are different depending on the phase of life you are in. Consider the frequency of sexual intercourse individuals will typically have when first starting to have sexual intercourse versus when someone gets married versus when someone is a lot older.

To uncover the frequencies of sexual intercourse in one's life I drew research done from the 2005 Durex Global Sex Survey. The results are based on a responses from almost 317,000 people worldwide. This is considered one of the most comprehensive sex surveys in the world.

According to the survey results, people aged 16-20 are engaging in 90 sexual experiences a year compared with 108 sexual experiences for 25-34 year olds, but the highest frequency of sexual intercourse is occurring for individuals aged 35-44 years with 112 sexual experiences a year.

Based on this data, I constructed a graph that would express the average amount of times per year an individual was having sexual intercourse at each age between 0 and 78.

Looking at the graph, I want to explain a couple features. First, the solid blue line is based on factual data that was attained and the black line is a polynomial function that best fits the data provided. The blue line is at 0 until age 17, because this is the first time that people engage in sexual intercourse on average according to documented research. Then, I graph the levels attained by Durex's Sex Survey for ages 16-20, 25-34, and 35-44. According to Durex, 35-44 year olds are having the "most" sex. Therefore, I consider the amount of 112 sexual intercourse experiences a year as my maximum and projected the data after the age of 44.

In order to make these projections, I found out that "Among 60- to 70-year-olds with partners, 46 percent of men and 38 percent of women have sex at least once a week" (HealthyMe). Therefore, I assume that at age 65 individuals are having 50 sexual experiences a week on average, which is a decline of 2.95 sexual experiences per year from 45 years old to 65 years old.

I then assume that at age 78 there are no longer any opportunities for sexual intercourse, on average, and therefore find the rate of decline from 50 sexual experiences at age 65 to 0 sexual experiences at age 78. This is a decline of 3.85 sexual experiences per year, on average.

Using the Trendline tool in Excel, I fit the graph that I had constructed with a binomial function that could generally explain for the amount of sexual intercourse an individual has per year, on average, based on the research I had collected.

The binomial function is equal to:

Where x is equal to the age of the individual. Using this formula, I was able to figure out the amount of times per year an individual has sexual intercourse from age 17 through 78, on average, for each year.

In order to figure out how many times during a lifetime an individual will likely have sexual intercourse, I find the sum of the frequency of sexual intercourse episodes a year for each year from 17 through 78. This is expressed as:

Performing this calculation, I arrive at a total of 4835.05 instances of sexual intercourse over the average lifetime for the average individual in the United States.

But, I am not done yet. I now need to find out how much time this equals. According to the Durex Global Sex Survey, "Americans spend 35 minutes on foreplay and sexual intercourse each session" (Source).

Therefore, by simply multiplying 4835.05 by 35 minutes, I arrive at the total amount of time having sexual intercourse in minutes for the average American. The amount of time spent having sexual intercourse over the average lifetime is therefore: 169,226.8 minutes.

This value is equal to 2820.4 hours and 117.5 days. In terms of an individual's average lifetime, the amount of time having sexual intercourse only equates to 0.41% of total life activities, on average.

• Conclusion

In order to figure out the amount of time an individual has sexual intercourse over a lifetime in the United States on average, I found out when people start having sexual intercourse and what the average life expectancy is. This gives an average "window of opportunity" for sexual intercourse.

Then by researching the frequencies of sexual episodes per year for various age segments of the population, I was able to determine a binomial function that expresses the amount of sexual experiences had for each year during the "window of opportunity."

I then added these to arrive at the average amount of sexual intercourse experiences had in a lifetime. I found that it was approximately 4835 sexual intercourse experiences in an average American lifetime.

I then found out the average length of time a sexual intercourse experience lasts, 35 minutes, and multiplied this number by the amount of sexual intercourse experiences over an average lifetime.

This calculation gives us our answer to the brain teaser, "How much time does the average person engage in sexual intercourse during their lifetime?" The determined value is 169,226.8 minutes or 2820.4 hours or 117.5 days or 0.41% of the average person in the United States' life.