A person was born on may 14, 40 B. C. and died on may 14, 30 A. D. how many years did this person live.

This can be a trick question.

You can treat this problem as a problem of subtraction of integers.

Let B. C. years be represented by negative integers, and let A. D. years be represented by positive integers. Then you subtract.

40 B. C. is - 4030 A. D. is 30

Then you have 30 - (-40) = 30 + 40 = 70

So far it's straightforward, and it seems the person lived for 70 years.

Here comes the (possible) trick with this question.

There was no year 0.

The counting of the years started with year 1, then year, 2, etc.

When we account for years before the year 1 A. D., the closest year to 1 A. D. is 1 B. C., not the year 0.

Since there is no year 0, then you must subtract 1 year from our calculation above, and the person lived 69 years.