A generation is about one-third of a lifetime.

[Bijackar]

Homework Statement

A generation is about one-third of a lifetime. Approximately how
many generations have passed since the year 0 AD?

Let me first say that this is my first time taking physics and this is all new to me so I appreciate all the help.

Homework Equations

here is the answer I found by googleing but I don't quite understand it. I was wondering if someone could explain it to me.

history x (10^11s / history) × (1 generation / 1/3 lifetime) × (0.5 lifetime / 10^9s) = 150

The Attempt at a Solution

How I approached this problem was that I chose 70 to be an average person's lifetime then I divided that by 3 to find what a generation is and then divide 2015 by that number which is not what the answer says. I think I just don't get the question.

 

[SammyS]

Homework Statement

A generation is about one-third of a lifetime. Approximately how
many generations have passed since the year 0 AD?

Let me first say that this is my first time taking physics and this is all new to me so I appreciate all the help.

Homework Equations

here is the answer I found by googleing but I don't quite understand it. I was wondering if someone could explain it to me.

history x (10^11s / history) × (1 generation / 1/3 lifetime) × (0.5 lifetime / 10^9s) = 150

The Attempt at a Solution

How I approached this problem was that I chose 70 to be an average person's lifetime then I divided that by 3 to find what a generation is and then divide 2015 by that number which is not what the answer says. I think I just don't get the question.

Looking at that "Googled" solution:

What time interval are they assuming for the "history" of whatever?

What time interval are they assuming for a "lifetime" ?

 

[Bijackar]

There aren't any information. Here is the link:

http://www.learningpod.com/question...how-many/6043291e-505a-425c-8311-1714a1f535ee

 

[SammyS]

Look at their expression.

(10¹¹s / history) is a conversion factor for units of "history" to seconds.

How many years are there in 10¹¹ seconds?


Similarly, (0.5 lifetime / 10⁹s) is a conversion from seconds to a "half a life(time)".

How many years are in 10⁹ seconds?

 

[TheAustrian]

A "Generation" is commonly 25 years. The Question is asking how much (unknown variable) multiplied by 25 gives 2015?

 

[SammyS]

...

How I approached this problem was that I chose 70 to be an average person's lifetime then I divided that by 3 to find what a generation is and then divide 2015 by that number which is not what the answer says. I think I just don't get the question.

By the way, I should have said:

Welcome to PF!


AND --

Your method is perfectly reasonable.

I was merely trying to get you to understand some of the quantities in that expression you found elsewhere.