Advent calendar 2015
16 December
Today's number is four thirds of the average (mean) of the answers for 13th, 14th, 15th and 16th December.
Show answer
Hide answer
Let today's number be \(n\). The average is:
$$\frac{729+313+328+n}{4}$$
Therefore:
$$\begin{array}{rl}
\frac34n&=\frac{729+313+328+n}{4}\\
3n&=729+313+328+n\\
2n&=729+313+328\\
&=1370\\
n&=685
\end{array}$$