1 00:00:05,110 --> 00:00:06,050 Hi everybody! 2 00:00:06,380 --> 00:00:08,620 This is Jason again from Collaborative Mathematics. 3 00:00:08,790 --> 00:00:10,500 This is Challenge Video number 2. 4 00:00:11,650 --> 00:00:14,370 Thanks, first of all, to everybody who has participated so far. 5 00:00:14,540 --> 00:00:19,990 Thanks to all of the Twitter-followers, and Facebook-likers, 6 00:00:20,130 --> 00:00:21,730 and YouTube-subscribers that we’ve gotten. 7 00:00:22,080 --> 00:00:26,840 Thanks to the three people who uploaded video responses to Challenge Video 8 00:00:27,010 --> 00:00:30,080 number 1, so far. That was really cool. 9 00:00:30,370 --> 00:00:33,760 And thanks also to people who have done the problem and haven’t uploaded 10 00:00:33,920 --> 00:00:35,640 videos. 11 00:00:35,820 --> 00:00:36,820 I’ve heard from people who have just done 12 00:00:37,000 --> 00:00:38,190 it at their desks, individually. 13 00:00:38,400 --> 00:00:42,450 And some teachers who have done the challenge with groups of students. 14 00:00:42,850 --> 00:00:45,210 All of that is really fantastic and I appreciate 15 00:00:45,490 --> 00:00:46,700 everybody’s participation. 16 00:00:46,990 --> 00:00:48,970 I hope to see some more participation with 17 00:00:49,160 --> 00:00:50,120 Challenge number 2. Here it is! 18 00:00:50,430 --> 00:00:51,680 I’ve got my calculator here. 19 00:00:51,880 --> 00:00:55,940 Notice that when I take the number 1089 20 00:00:56,900 --> 00:00:58,670 and I multiply by 9 21 00:01:00,630 --> 00:01:03,960 I get 9801. 22 00:01:05,630 --> 00:01:07,070 "Who cares?" you say. 23 00:01:07,360 --> 00:01:08,250 But check it out! 24 00:01:08,440 --> 00:01:16,190 That’s the same number, it’s just been flipped. 25 00:01:16,440 --> 00:01:20,020 1-0-8-9 becomes 9-8-0-1. 26 00:01:20,340 --> 00:01:21,270 That’s cool. 27 00:01:21,580 --> 00:01:23,270 And it doesn’t happen, generally speaking, right? 28 00:01:23,510 --> 00:01:27,560 If I picked another four-digit number and I multiply by 9, 29 00:01:27,780 --> 00:01:32,790 like if I took 2658 times 9, I get something else. 30 00:01:32,990 --> 00:01:34,340 It doesn’t flip around. 31 00:01:34,690 --> 00:01:36,540 So something interesting is happening in the first case 32 00:01:36,770 --> 00:01:38,650 that is not happening in the second case. 33 00:01:38,850 --> 00:01:39,620 So let’s name that. 34 00:01:39,990 --> 00:01:46,510 Let’s say that the number 1089 is "flipped when multiplied by 9". 35 00:01:47,880 --> 00:01:51,390 Then, the core challenge for this video is: 36 00:01:51,900 --> 00:01:58,210 Which four-digit numbers are flipped when multiplied by 4? 37 00:01:58,630 --> 00:02:00,190 So that’s the core challenge, but of course, 38 00:02:00,590 --> 00:02:04,270 that question might make you wonder about other things, too. 39 00:02:04,580 --> 00:02:10,830 Is 1089 the only four-digit number that is flipped when multiplied by 9? 40 00:02:11,270 --> 00:02:15,700 Are there any 3-digit numbers that are flipped when multiplied by 9? 41 00:02:15,940 --> 00:02:19,000 Or 5-digit numbers that are flipped when multiplied by 9? 42 00:02:19,170 --> 00:02:20,880 Or when multiplied by 4? 43 00:02:21,720 --> 00:02:23,550 What happens when you multiply by 3? 44 00:02:23,870 --> 00:02:26,380 Can you get a number that is flipped when multiplied by 3? 45 00:02:26,510 --> 00:02:27,300 Or by 7? 46 00:02:27,530 --> 00:02:28,430 Or by 13? 47 00:02:28,790 --> 00:02:32,060 There’s lots to be curious about in this area, 48 00:02:32,290 --> 00:02:36,160 so I say explore whatever you find interesting and then upload a response 49 00:02:36,360 --> 00:02:40,520 video with your observations, and discoveries, and any other questions 50 00:02:40,700 --> 00:02:42,130 that come to mind! 51 00:02:42,970 --> 00:02:44,320 Check us out online. We’re at 52 00:02:44,510 --> 00:02:46,160 Collaborative Mathematics . org 53 00:02:46,400 --> 00:02:50,490 There can find little social media buttons that will connect you to our pages on 54 00:02:50,790 --> 00:02:53,850 Facebook, and Google Plus, and Twitter, and YouTube. 55 00:02:54,100 --> 00:02:58,560 So that you can follow, and like, and subscribe to what we’re doing here at 56 00:02:58,740 --> 00:02:59,630 Collaborative Mathematics. 57 00:03:00,060 --> 00:03:03,330 Help us spread the word please, too. Tell your friends! 58 00:03:03,570 --> 00:03:06,260 And go out there and do some fun mathematics! 59 00:03:06,600 --> 00:03:08,710 I look forward to seeing what happens next!