Multiplication trick for fast calculation - By tecmath
Transcript
| 00:0-1 | Good day . Welcome to Tech Math Channel . What | |
| 00:01 | we're gonna be having a look at this video . | |
| 00:03 | It's a cool little trick on how to multiply numbers | |
| 00:06 | that are multiples of nine . I'll give you an | |
| 00:08 | example . These are numbers like 9 , 81 45 | |
| 00:16 | and had a little trip from multiplying with these numbers | |
| 00:19 | . Okay , so an example for this is as | |
| 00:21 | follows . So , So you've got a question about | |
| 00:24 | 43 times 27 . Now , look , this is | |
| 00:27 | just an interesting way of doing this . So the | |
| 00:30 | way Then I was showing you how to do is | |
| 00:32 | today these videos as five . So the first thing | |
| 00:35 | we do is we actually look at this number which | |
| 00:37 | is the multiple of nine , which is 27 . | |
| 00:39 | Okay . First off with multiple . Look at this | |
| 00:41 | one and this 19 goes into this three times . | |
| 00:44 | We're going to round this one up to the next | |
| 00:46 | tens number , which is going to be 30 . | |
| 00:48 | Okay , So it would do instead of 43 times | |
| 00:52 | 27 we would go 43 times 30 . Okay ? | |
| 00:56 | So the answer you're going to get to this is | |
| 00:57 | 12 90 . Okay ? So 43 12 and in | |
| 01:01 | the three threes in the 90 . Okay . Almost | |
| 01:04 | there then . What do we do ? You take | |
| 01:08 | 10% off ? 10% . Look at this number and | |
| 01:12 | divide it by 10 129 . We're gonna take this | |
| 01:15 | amount off . So if we would take 100 and | |
| 01:18 | 29 off this we're gonna get the answer . 1161 | |
| 01:24 | that's your answer . Yeah . Calls that . Okay | |
| 01:28 | . So you rounded up to the next tens number | |
| 01:30 | and then just take 10% off And it works Okay | |
| 01:33 | . It's a really good it works at any multiple | |
| 01:36 | nine number anywhere from 18 . Right up to 81 | |
| 01:39 | . Okay . So there's a couple of steps there | |
| 01:44 | . We ran up to the next tens were multiplied | |
| 01:46 | out and then we take that 10% off . Okay | |
| 01:49 | . Like I said , it's not the fastest one | |
| 01:50 | , but it's a pretty cool one . Anyway , | |
| 01:51 | so what about we do 65 times 18 . Again | |
| 01:57 | the number that we have right now identify the multiple | |
| 01:59 | . Normal . That's this one . Okay . We're | |
| 02:01 | gonna round this up there for 20 65 times 20 | |
| 02:06 | . The answer that is 1000 300 . Okay With | |
| 02:13 | the Middle Metal plate then . Okay . And from | |
| 02:16 | this we're going to take 10% off . Take 130 | |
| 02:19 | off . Okay . 130 taken off . This is | |
| 02:22 | 1179 . That's our answer . Okay . What about | |
| 02:27 | another one of those ? Mm . Okay . What | |
| 02:32 | about 24 times 63 ? Okay . I'm being very | |
| 02:39 | unimaginative . You're always putting the multiple and I number | |
| 02:41 | over here . Okay . And the next number above | |
| 02:43 | this is a 70 . Okay , so we end | |
| 02:45 | up with 24 times 70 . So how would you | |
| 02:49 | go with that sort of question ? 24 times 70 | |
| 02:51 | . We're gonna be adding uh the way I look | |
| 02:53 | at this as I'd probably thinking 1428 is going to | |
| 02:57 | be given the number of 16 , 80 . And | |
| 03:02 | we're gonna take 10 cent office . Okay ? Yeah | |
| 03:06 | , What answer we're gonna get to this ? Hopefully | |
| 03:09 | you're gonna get the answer of 15 12 . Cool | |
| 03:15 | . All right . What about we do a couple | |
| 03:21 | more of these then ? I'll show you something that | |
| 03:23 | is just a slight variation on this . Okay . | |
| 03:26 | Okay . To say we had 18 times 27 . | |
| 03:31 | Now what you're gonna notice with this is both of | |
| 03:33 | these numbers here Multiples of nine . You know this | |
| 03:36 | is this goes in twice and this one goes in | |
| 03:38 | three times . Okay ? So say we would okay | |
| 03:42 | which one we choose . We can choose any one | |
| 03:44 | of these . We could say let's choose this one | |
| 03:46 | and rounded up to 30 . Or we could have | |
| 03:50 | rounded this one and then taken the 10% off . | |
| 03:52 | We could have rounded this one up to 20 times | |
| 03:56 | by 27 . And let's have a look at the | |
| 03:57 | result here . You're going to notice them for both | |
| 03:59 | of these . What we do is we end up | |
| 04:02 | with 540 . These both equal 540 . Okay , | |
| 04:07 | so it doesn't matter which one we do , but | |
| 04:09 | I'll show you a step further . You can go | |
| 04:11 | with this in a second . Okay ? So say | |
| 04:12 | what you can do here is you can go okay | |
| 04:14 | now take off 10% of the take off 50 for | |
| 04:17 | and this gives us the answer of 486 . Okay | |
| 04:22 | So it doesn't actually matter which one you choose with | |
| 04:24 | this . Uh Just I just want to show you | |
| 04:27 | this this thing I was thinking before okay this this | |
| 04:29 | next step that you can go with this . So | |
| 04:31 | so you think well stuff that I'm gonna rare both | |
| 04:35 | of them , Okay I'm gonna end up with 20 | |
| 04:37 | times 30 . So we do that and we end | |
| 04:39 | up with the answer of 600 . So we take | |
| 04:42 | 10% off that 10% is 60 . We're gonna end | |
| 04:45 | up with 5 40 . Take 10% off again , | |
| 04:49 | We get our answer okay ? Which is going to | |
| 04:51 | be 486 . So what we do is we do | |
| 04:54 | the same thing , we can round it up . | |
| 04:55 | We ran up both we have to take off 10% | |
| 04:57 | twice . Okay . What about one last one of | |
| 05:01 | those were the ones ? Okay . What about I | |
| 05:04 | give you 27 81 . Okay . 27 times 81 | |
| 05:11 | . Okay Let's round both of them are let's get | |
| 05:13 | really really of interest here . Round both up to | |
| 05:16 | 30 times 90 and we're gonna get this answer . | |
| 05:20 | $3.27 2,702,700 . Take off 10% which is 2 70 | |
| 05:28 | . Okay . That's going to give us the answer | |
| 05:29 | of 2403 and take off 10% which is 243 . | |
| 05:38 | And that is going to give you a wonderful , | |
| 05:40 | wonderful , wonderful answer of 2,187 . Now look at | |
| 05:47 | the very least with this you've got to say it | |
| 05:49 | gets you practicing your 10% which is really really good | |
| 05:52 | anyway . Okay I think a lot of people should | |
| 05:54 | practice percentages a fair bit . Okay . But it's | |
| 05:57 | a cool little trick . Is it the fastest trick | |
| 05:59 | ? Okay . The jury everybody's out on that one | |
| 06:03 | , but I reckon it's a pretty cool one anyway | |
| 06:04 | , tell us what you think with this anyway . | |
| 06:07 | Thanks for watching . See you next time . |
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