NapkinCalc

Pre-Algebra — Numbers & First Variables

Integers & signed numbers

continues from lesson 1 — values defined earlier in the course stay live here

ELI5: integers include the negatives below zero. Two rules trip everyone up:

  • a negative times a negative is positive (−3 × −4 = 12)
  • subtracting a negative adds (5 − (−2) = 7).
✓ pass (−3)∗(−4)==12(-3) * (-4) == 12 two negatives make a positive
✓ pass 5−(−2)==75 - (-2) == 7 subtracting a negative is adding

Real-world hook: signed numbers are temperatures below zero, bank balances in the red, and elevations below sea level.