A parent is 3 times as old as their child. Together they are 84. How old is each?
The child is 21 and the parent is 63.
How to work it out
- 1
Let x be the child's age. The parent is 3 times as old, so the parent is 3x.
- 2
Together they are 84:
- 3
Combine the x terms and divide:
- 4
The parent is 3 × 21 = 63.
- 5
Check: 21 + 63 = 84 ✓ and 63 = 3 × 21 ✓.
LaTeX source of the formulas on this page
\[ x + 3x = 84\ \Rightarrow\ x = 21 \]
\[ x + 3x = 84 \]
\[ 4x = 84\ \Rightarrow\ x = \frac{84}{4} = 21 \]Questions
How old is the child?
21.
How old is the parent?
63.