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## Early math review

### Course: Early math review > Unit 3

Lesson 1: Teens# Teen numbers: monkeys

Sal breaks the number 18 into 10 and 8. Created by Sal Khan.

## Want to join the conversation?

- what is 567490005 + 2330009987=(8 votes)
- So knowing place value makes adding subjects easier?(5 votes)
- Nope it makes it million times harder than ever before!(3 votes)

- you need 8 monkeys to make 18(5 votes)
- You are on the right track. You need 8 monkeys and an additional 10 monkeys to make 18 monkeys. 8+10=18(1 vote)

- How do you count in binary, and what is 18 in binary?(1 vote)
- I think
*@Jerry Nilsson*did a great job explaining how to write in binary, but he never went over what binary is, and why we do it the way we do it.

The**binary**number system is a**base 2**number system. That means that each place value is**two times more than**the last place value. For example, we may have ones, tens and hundreds, and binary may have, ones, twos, fours, eights, and so on.

Being a base 2 number system also means it consists of two characters,*or symbols.*These symbols are**ones and*** zeros*. This means we add another place value every time one of the numbers becomes**greater than**the largest digit, which is**one**.*(In base ten, what we write in, the largest digit is***9**)

So instead of counting like`0, 1, 2, 3, 4, 5, 6, etc.`

, binary counts like this;`0, 1, 10, 11, 100, 101, 111, 1000, 1001, 1011, 1111, etc.`

So instead of adding another digit after**9**,`(6, 7, 8, 9,`

, we add another digit after the number**10**)**1**.`(0, 1,`

.**10**)

I hope this helped! Let me know if you still have any more questions about this!(2 votes)

- Would the same idea work for hundreds?(3 votes)
- Yes the same idea should work for hundreds. However if you where to work with monkeys you would have quite a few monkeys on your hand.(2 votes)

- 10+8=18 and 1234567891011121314151618(3 votes)
- Who invented desmels? All so why do we even need desmels, what do they don't help use with anything.(2 votes)
- decimals are used for exact numbers mainly used for dividing and look like this: (this is only an example and not the only way to use decimals) 10.0904

You will learn about decimals in 5th grade math(2 votes)

- Los 1 de los numeros son los tens(2 votes)
- what is 999 + 999(2 votes)
- 999+999=1000-1+1000-1=2000-2=1998(2 votes)

- is zero the last number in the numbers?(2 votes)
- There are an infinite amount of numbers! Even ones below 0. They are called negative numbers. Before 0 is negative 1, and before negative 1 is negative two. Here is a number line that might help.

-5 -4 -3 -2 -1 0 1 2 3 4 5

|---|---|---|---|---|---|---|---|---|---|---|---|

I started at -5, but there are many more numbers before that. Think of it in terms of cookies. Maybe there were 2 cookies. One for you and one for your friend. But, your friend took your cookie. So now, they owe you a cookie. This is the same as saying the have -1 cookies. They have two cookies, they owe you one. Now they have one cookie. That is the same as 2 plus -1. Or, just 2 minus 1. Crazy, right?(2 votes)

## Video transcript

Voiceover:Let's say that
you're throwing a party, and as we all know, any party needs a sufficient number of monkeys. Right now you have 10 monkeys. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. But you would like to have 18 monkeys. How many more monkeys do you need in order to have 18 monkeys? I encourage you to pause the video and think about it on your own before I work through it. Remember, the goal here is to get to ... The goal here ... Let me write it this way. The goal here is to get to 18, 18 monkeys. Now what do we know about the number 18? Well the number 18, you have this 1 right over here in the tens place. That literally represents 1, 10. And then this 8 represents 8, 1's. Plus 8, 1's. That's the same thing as saying 1, 10 ... 1, 10, that's just a 10 right over there. And 8, 1's, that's just 8. 18 is the same thing as 10 plus 8. If we start with 10
monkeys, which is how many we have started with, how many more do we need to get to 18? Well, if you start at 10, you need 8 more to get to 18. We can verify that visually, if we like. Let's see. Let me copy and paste 1 of these monkeys. Copy. This is 10. Now, let's get to 18. 11, 12, 12, 13, 14, 15, 16, 17, and 18. And 18. How many more did we add? Well, once again, we started, we started with this 10 right over here. Let me box them off. We started with these 10 monkeys. That's 1 group of 10 right over there. We started with the 10. And then we added 8 more monkeys. 1, 2, 3, 4, 5, 6, 7, 8. 1, 2, 3, 4, 5, 6, 7, 8. So we started with 10. We added 8 more monkeys. We added 8 more monkeys
to get, to get to 18. And once again, how did we first think about that? Well, 18 is 1, 10 plus 8, 1's. Or 10 plus 8.