Awkward question - pairing average for two different types of elements where ratio is 1:1 Not sure if this is adequate for math.stackexchange but please let me know and I will delete it. I've tried to make it more abstract, but then it would raise more questions than give answers. I've come across a statistic where it says that men have slept on average with 13 women in their lifetime, and women with 7 men. Now, I know that this is not reliable information and so on but let's make the following presumptions: Man/Woman ratio is 1:1 Only type of coitus is in a heterosexual pair People don't lie in this sort of studies When two people pair up, it counts for both Is there any possibility for this? I just can't wrap my head around it, and would appreciate any sort of suggestions.

It is only possible if the study had excluded people who had never got laid. Consider the following situation:

**Key** : $\color{red}{\text{red}}$ is woman, $\color{blue}{\text{blue}}$ is man

!man woman

If the lonely men are ignored, then men on average have slept with $(2+3+2)/3 \approx 2.333$ women (notice that it is divided by $3$, not $6$); while women on average have slept with $(1+2+1+1+1+1)/6 \approx 1.667$ men.

However, if the lonely people are considered when computing the average, then yes, the value for both sexes must be the same. One way to see this is to observe that the number of lines "coming out" from each sex must be the same, along with the fact that man/woman ratio in the human population is very close to $1:1$.