Copyright © University of Cambridge. All rights reserved.

'Baby's Weight' printed from https://nrich.maths.org/

Show menu


Let $m$ be my weight, $b$ be the baby's weight and $n$ be the nurse's weight.

We have
$$
\begin{align}
m+b&=78\\
b+n&=69\\
m+n&=137\;.
\end{align}
$$
We can add all three equations together like this:
$$(m+b)+(b+n)+(m+n)=78+69+137\;.$$
It follows that $2(m+b+n)=284$ and hence $m+b+n=142$. So the combined weight is $142\;\mathrm{kg}$.

For an extra challenge can you find the weights of each person?

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.