Teen numbers: monkeys

0:00Voiceover: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?

0:23I 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?

0:44Well 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.

1:1018 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.

1:36Copy. 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.

2:22We 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.

2:54Or 10 plus 8.