B1. Polly Garter had her first child on her 20th birthday, her second child exactly two years later, and her third child exactly two years after that.
How old was Polly when her age was equal to the sum of her three children's ages?
Solution
Let Polly be $x$ years old when her age was equal to the sum of her three children's ages. At this time, her three children were $x-20, x-22$ and $x-24$ years old. This leads to the equation
$$
x=x-20+x-22+x-24 \text {. }
$$

Hence
$$
\begin{aligned}
x & =3 x-66 \\
2 x & =66 \\
x & =33 .
\end{aligned}
$$

Therefore, Polly was 33 years old when her age was equal to the sum of her three children's ages.