If 72% percent of new apps are reviewed within the last 7 days, then there is a 72% chance that any app is reviewed in the last week.
$$72\% = \sum\limits_{i = 0}^{6} {x\left( {1 - x} \right)^i }$$
where $x$ represents the probability that an app is reviewed each day.
If $p = \left( {1 - x} \right)$, then the following is true:
$ \eqalign{ & 72\% = x + xp + xp^2 + xp^3 + xp^4 + xp^5 + xp^6 \cr & 72\% = x\left( {1 + p + p^2 + p^3 + p^4 + p^5 + p^6 } \right) \cr & 72\% = 1 - p^7 \cr & p^7 = 1 - 72\% \cr & p^7 = 28\% \cr & \left( {1 - x} \right)^7 = 28\% \cr & 1 - x \approx 0.8337 \cr & x \approx 16.63\% \cr} $
Is my work correct?