First, we need to determine how many slices the pizza was cut into. To do this, we start by performing 1*2= <<1*2=2>>2 slices after the pizza was cut in half once.
Each of these slices was cut in half again, yielding 2*2= <<2*2=4>>4 slices in total.
Next, we divide the total amount of pepperoni slices by the number of pizza slices, as the pepperoni was spread evenly. We find there are 40/4= <<40/4=10>>10 slices of pepperoni per pizza slice.
Since 1 slice of pepperoni fell off Jelly's slice, this means there are 10-1=<<10-1=9>>9 slices left on her slice.
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