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Lesson 5: Teens

# Teens as sums with 10

Sal looks at the 1 in each teen number and thinks about what it really means.  Created by Sal Khan.

## Want to join the conversation?

• Why does it say 11 and 12 are teen numbers? They don't have teen in it's name.
• Teen numbers are numbers in the range of 11-19.
• why something over zero is infinity?
• It's undefined. You can try to divide something, say number 5 by 0,0001 you would get a very high number. You may then be tempted to think that the closer the denominator gets to zero the higher the result is going to be therefor going to be infinity.
However try the exact sam number 5 and divide it by -0,0001 you would get a very large Negative number. Therefor you could equally conclude when the denominator closes in to zero from the negative side you would reach negative infinity.
In short: The argument that dividing by zero is infinte is wrong, it IS undefined.
• Will they ever be a bigger place value chart? So if I have 789456123 what would be the place value chart
• The point of a place chart is to help you count numbers. Eventually you won't need place charts anymore. But if there was a place value chart and the number 789456123 was in there, then the place value chart would begin at 100, 000, 000 and end at 999, 999, 999.
• what is the history of numbers
• From my understanding, there is no true origin of numbers that historians can claim to be. Trying trace the humanity history, number existed way before as a means of communication and measurement just that it was interpreted differently in different societies. Take a look from the historian point of view. Ancient greek symbols like pie, alpha, beta e.t.c and the roman symbols came to interpreted as numbers in the modern contemporary English. Good question.
• why did you only count to 20?
• because this video is about teen numbers
• Why do you have to watch videos
• Watching videos helps you better understand what's happening.
• some math is inpossible but you can try to do the math so your grades can be up
• So you can lean later in the future so you know.
• I dont understand comen core math why do they make it so hard to awnser the simplist problem