A person is 80 years old in 490 BC and only 70 years old in 500 BC. In which…

Concept: In the BC (Before Christ) era, years count downward toward 1 BC as time moves forward, so a BC year that occurs later in time has a smaller BC number. If a person's age is known in a particular BC year, the person's birth year (in BC) is found by adding that age to the BC year number, since the person was born that many years before that BC year.

1. The person is 70 years old in 500 BC and 80 years old in 490 BC. Since 490 BC comes 10 years after 500 BC, and the age also increases by 10 years (70 to 80) over that span, the two data points are consistent with each other.

2. Using the 500 BC data point: birth year = 500 + 70 = 570, i.e., BC 570.

3. Using the 490 BC data point as an independent check: birth year = 490 + 80 = 570, i.e., BC 570 — the same result confirms the answer.

Hence, the person was born in BC 570.