Determining the Birth Year of a 12-Year-Old from 2020-2021

When faced with the question of determining the birth year of a 12-year-old born in 2020 or 2021, many find it quite challenging to do the calculation mentally. Let’s break it down step-by-step to ensure clarity and accuracy.

Step-by-Step Calculation

First, we need to understand that a 12-year-old in 2020 or 2021 would have been born in 2008 or 2009, based on the given information. Here's why:

For 2020:

December 31, 2020

If someone was born on or before December 31, 2010, they would be 11 years old in 2021. Therefore, to be 12 years old in 2020, they must have been born in 2008.

January 1, 2020

If someone was born on or before January 1, 2012, they would be 11 years old in 2021. Therefore, to be 12 years old in 2020, they must have been born in 2009.

For 2021:

December 31, 2021

If someone was born on or before December 31, 2013, they would be 11 years old in 2022. Therefore, to be 12 years old in 2021, they must have been born in 2009.

January 1, 2021

If someone was born on or before January 1, 2022, they would be 11 years old in 2022. Therefore, to be 12 years old in 2021, they must have been born in 2009.

Common Misunderstandings

Sometimes, people get confused because they mistakenly think that if the individual is 12 in 2020 or 2021, their birth year should be directly subtracted by 12 from the current year. However, this approach often leads to incorrect results. It's crucial to consider the specific month they were born in to accurately determine their birth year.

Solving Common Questions

1. If they are 12 years old in 2020:

Born in 2008: If born on or before December 31, 2008, they would turn 12 by the end of the year. Born in 2009: If born on or before January 1, 2009, they would turn 12 by the end of the year.

2. If they are 12 years old in 2021:

Born in 2009: If born on or before December 31, 2009, they would turn 12 by the end of the year. Born in 2009: If born on or before January 1, 2009, they would turn 12 by the end of the year.

Conclusion

As we can see, the birth year of a 12-year-old born in 2020 or 2021 depends on the specific date of birth. If they were born on January 1st, the calculations for 2020 and 2021 would be as follows:

2020: 2020 - 12 2008 (December 31, 2020) 2021: 2021 - 12 2009 (January 1, 2021)

It's important to note that these calculations consider the month of birth to ensure accurate results.