Metro mean and variance

At the metro every few weeks I run into a nice example of the difference between mean and variance. My card is running out of credit, so I figure I should recharge it. Now, should I do that before the train ride, or after?

If I recharge the card after the ride, it will take one minute, and that’s that. The mean time spent is one minute and the variance is zero.

If I recharge it before, it’s a lottery. Nine times out of ten, I’ll catch the same train, so I’ll lose zero minutes. The tenth time, I’ll miss the train and spend ten minutes waiting for the next one. The mean is exactly the same, one minute! — but the variance is far from zero.

So which is the right choice? Ah, that depends on my day’s schedule and my mood and my personality. There’s nonlinearity for you.

[24 March 2018]

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s