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A parent is 2 times as old as their child. Together they are 21. How old is each?

The child is 7 and the parent is 14.

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How to work it out

  1. 1

    Let x be the child's age. The parent is 2 times as old, so the parent is 2x.

  2. 2

    Together they are 21:

    x+2x=21x + 2x = 21
  3. 3

    Combine the x terms and divide:

    3x=21 ⇒ x=213=73x = 21\ \Rightarrow\ x = \frac{21}{3} = 7
  4. 4

    The parent is 2 × 7 = 14.

  5. 5

    Check: 7 + 14 = 21 ✓ and 14 = 2 × 7 ✓.

LaTeX source of the formulas on this page
\[ x + 2x = 21\ \Rightarrow\ x = 7 \]
\[ x + 2x = 21 \]
\[ 3x = 21\ \Rightarrow\ x = \frac{21}{3} = 7 \]

Questions

How old is the child?

7.

How old is the parent?

14.

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    Parent is 2 times the child's age, total 21: 14 and 7 | WordGPT