Bài toán tuổi

1. Spot an age problem

The question talks about the ages of two or three people. It asks about an age now, some years ago or some years later. Underline the numbers and the words "ago" and "later". These three things decide the method.

2. Draw age bars

Each person is one bar. The older person has the longer bar. The extra length is the age difference. Looking at the bars, you see at once who is older and by how much. Draw the bars on scrap paper before you calculate.

3. The difference never changes

Every year, everyone gets exactly one year older. So the age difference never changes. If Dad is 30 years older than you, he is always 30 years older. Ten years later, still 30. Ten years ago, also 30. Find the difference once and use it forever.

4. Ages some years ago or later

To find an age some years later, add the number of years. To find an age some years ago, subtract the number of years. If the question gives a future age, go back to now first. For example, in 5 years Alice will be 12. Now Alice is 12 minus 5, that is 7.

5. The sum of two ages

After some years, each person gains that many years. The sum of two ages gains twice the number of years. The sum of Wong's and Tan's ages is 8. After 5 years the sum gains 5 plus 5, that is 10. The new sum is 18.

6. Check your answer

Work out each person's age at the same moment. Then check the difference or the sum against the question. If everything matches, you are right. Read the question again to see whose age it asks for, and when.