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10, 9, 8...
Commander Alex is ready for launch! The countdown begins at 10 and counts DOWN to 0.
10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0... LIFTOFF!
Counting backwards is the same as subtracting 1 each time: 10-1=9, 9-1=8, 8-1=7...
What if the countdown starts at 20? 20, 19, 18, 17... same idea, just more numbers!
When we reach 0, that means none left - the countdown is DONE and the rocket launches.
**Think About It:** Zero is special. It means nothing remains. In a countdown, zero = GO!