Finite lifetime budgets become clearer when retained and lost counts are scanned. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The first row keeps four fifths
Prepared shots 100 split into retained 80 and lost 20. The retained fraction is 4/5.
80+20=100,fsurvive=54
The second row keeps seven tenths
The next budget keeps 84 of 120 prepared shots and loses 36. The exact fraction is 7/10.
84+36=120,fsurvive=107
The third row makes the loss larger
The third budget retains 52 and loses 28 out of 80 prepared shots. The scan ends at 13/20 survival.