Question

Counsuela is three times as old as Mary. In 10 years she will be only twice Mary's age. How old was Councuela 4 years ago?

Answer 1

Mary is x years old.
Consuela is three times as old as Mary, so she's 3x years old.
In 10 years Mary will be x+10 years old, and Consuela will be 3x+10 years old.
In 10 years Consuela will be twice Mary's age, so she'll be 2(x+10) years old.


`3x+10=2(x+10) \\ 3x+10=2x+20 \\ 3x-2x=20-10 \\ x=10 \Leftarrow \hbox{Mary's age} \\ \\ \hbox{Consuela's age:} \\ 3x=3 * 10=30`

Now Consuela is 30 years old.


`30-4=26`

4 years ago Consuela was 26 years old.