A parent is 5 times as old as their child. Together they are 90. How old is each?
The child is 15 and the parent is 75.
How to work it out
- 1
Let x be the child's age. The parent is 5 times as old, so the parent is 5x.
- 2
Together they are 90:
- 3
Combine the x terms and divide:
- 4
The parent is 5 × 15 = 75.
- 5
Check: 15 + 75 = 90 ✓ and 75 = 5 × 15 ✓.
LaTeX source of the formulas on this page
\[ x + 5x = 90\ \Rightarrow\ x = 15 \]
\[ x + 5x = 90 \]
\[ 6x = 90\ \Rightarrow\ x = \frac{90}{6} = 15 \]Questions
How old is the child?
15.
How old is the parent?
75.