NapkinCalc

Start Here — A Complete Tour

Sums, products & the formula library

continues from lesson 6 — values defined earlier in the course stay live here

For "add this up over a range," use Sum (capital S): Sum("expression", "index", start, end) — the expression and index go in quotes. Prod is the same for multiplication. You never have to type these from memory: the Σ Formulas button in the toolbar opens a searchable library of ready-made formulas you can drop in.

gausssum:=Sum("i","i",1,100)gauss_{sum} := Sum("i", "i", 1, 100) = 50505050 1 + 2 + ⋯ + 100, the long way
✓ pass gausssum==5050gauss_{sum} == 5050 Gauss was right
fivefactorial:=Prod("i","i",1,5)five_{factorial} := Prod("i", "i", 1, 5) = 120120 5! = 1·2·3·4·5
✓ pass fivefactorial==120five_{factorial} == 120