update challenge display

Author: avallecam

episodes/superspreading-estimate.Rmd

@@ -736,7 +736,9 @@ Review how we estimated the probability of having clusters of a fixed size, give
 
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 ```{r}
 # estimate the probability of
@@ -755,8 +757,6 @@ The probability of having clusters of five people is 1.8%. At this stage, given
 
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 ## Challenges
 
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