View Full Version : Can you multiply 43 and 52 in your head?

Checkboard

14th May 2013, 20:19

43 times 52 = 2236

In my head.

15 and 8 is 23.

4*5 is 20, plus 2 is 22

next is the 3

2*3 is 6

Put it together is 22 3 6

Any Aussie would know that! Why isn't it taught in schools here in the UK? :confused:

Fast Math Tricks - How to multiply 2 digit numbers up to 100 - the fast way! - YouTube

;)

Dushan

14th May 2013, 20:30

There is an easier way:

43x52

4300/2 = 2150

2150 + 86 = 2236

.

.

Eric T Cartman

14th May 2013, 20:30

The way I was taught was to do 43x5, stick a 0 on the end & add 43x2 - mind you that was in about 1955 ! ;)

toffeez

14th May 2013, 20:32

100 x 43 = 4300

so 50 x 43 = 2150

add 2 x 43 = 86

2150 + 86 = 2236

ExSp33db1rd

14th May 2013, 20:33

Toffeez - beat me to it whilst I was writing it !!

Took about 10 secs. ( less time than it takes to write it below )

50 x 43 = ( 43 x 10 / 2 = 215 x 10 = 2150 ) + ( 2 x 43 = 86 ) = 2236.

Don't even need a calculator to work out the cost of 2 x packages of cornflakes in the supermarket at $2.99 each - but the young cashier does.

cuefaye

14th May 2013, 20:33

Of course I can, I'm a fighter pilot - or was. Got a while?

toffeez

14th May 2013, 20:42

I think you'll agree, for anyone born before calculators and computers this is a piece of piss.

Before decimal currency, old ladies could swirl pounds, shillings, and pence around in their head and never get cheated.

There's another thread about whether the victorians were more intelligent ...

.

TURIN

14th May 2013, 20:57

The way I was taught was to do 43x5, stick a 0 on the end & add 43x2 - mind you that was in about 1955 !

Me too, mid seventies though.

My education not my age.:O

dead_pan

14th May 2013, 21:47

Partition(?) as follows: (40 + 3) x (50 + 2)

Multiply through to get: (40 x 50) + (40 x 2) + (50 x 3) + (2 x 3)

Easy-peasy from then on.

spInY nORmAn

14th May 2013, 21:58

So I went at it thusly:

40 x 50 = 2000

3 x 52 = 156

40 x 2 = 80

Then add 'em up!

The comment about pounds shillings and pence reminded of when I worked as a teen at the fruit and veg counter in the food hall of a department store in Edinburgh in the 60s. You would weigh all the items out on the scale and keep a running total in your head (some used to write them down on a paper bag but that was considered cheating). Most of the time you got it spot on but occasionally you were admonished by some old wifey with a "Ah dinnae think ye got that right, son!" They were usually correct!

How quickly can you still add up:

7/6

4/5

6/3

1/11

3/2

Bob Lenahan

14th May 2013, 22:00

Well, I go 52 (4) = 208 and add the 0 so you get 2080

and

52 (3) = 156

so

2080 + 150 = 2230 + 6 = 2236.

You can skip the 150 by going 2080 + 156.

Or, you can ...

Bob.

Cacophonix

14th May 2013, 22:00

So you know when to divert...

Forget about how much it is hurting...

Caco

Cacophonix

14th May 2013, 22:08

4 * 500

2000

You already know where you are....

You will put it down without a tear in your eye...

Caco

G-CPTN

14th May 2013, 22:14

My father was the Man from the Prudential collecting cash for weekly and monthly insurance (and assurance) premiums from customers (at their homes).

The amounts collected for each policy were written into his collecting book (as well as the customers' own 'rent books'),

At the end of each day he would add up each page of LSD figures and he could count using base 12 as easily as base 20. Then the cash was counted and had to balance!

Cacophonix

14th May 2013, 22:19

Fly a DME approach in a light twin at night, alone and don't **** it up...

The simple rumble of honest wheels...

Caco

DX Wombat

14th May 2013, 22:31

Of course I can. I was teeched proper like wot Eric woz.

Tankertrashnav

14th May 2013, 23:14

Scene - St Aloysius school, Langside, Glasgow, sometime in 1957 at 9 am

A class of 10 year olds awaits the entrance of form teacher Mr Tollan.

Mr Tollan enters. "Sixteen times table, odd numbers only, backwards, begin!"

Thirty boys start to chant "Sixteen fifteens are two hundred and forty, sixteen thirteens are two hundred and eight, etc", each praying they don't get any wrong, thus incurring a smack on the head from Mr Tollan (a borderline psycho, I now realise).

That's why like the rest of you I can do this without really thinking about it!

Spiny £1-3-3d - wis I right? ;) (around 10 seconds)

spInY nORmAn

14th May 2013, 23:35

Tankertrash - £1-3-3d is correct - you're hired!

Fox3WheresMyBanana

14th May 2013, 23:57

Bulldog - Spinning III, going well. Going far too well for my QFI in fact (ex-CFS Trappers).

"Spin left please."

"Check height, 8,500', Check direction,...blah"

"Count down from 243 in 17's as well"

"What?? er Height 7,500, 2 turns, speed good, two hundred and..26, check sun.....two hundred and..9"

etc.

Love that workload!

Got to thank him tho'...I made FJ like he did. To quote my IOT F/S

"You know it makes sense!"

helicopterray

15th May 2013, 02:46

Here's another method.

The magic of Vedic math. [VIDEO] (http://www.wimp.com/vedicmath/)

Tarq57

15th May 2013, 03:33

Turns out I can.

My rather cumbersome method was to first get an approximation of the answer (40 X 50 = 2000, and a bit) then to imagine doing it on the blackboard, the "long" way, the way my arithmetic teacher taught me in what is now called year 3 or thereabouts.

Took about 2 minutes. Could do it faster, I suppose.

alisoncc

15th May 2013, 03:57

Dushan There is an easier way:

43x52

4300/2 = 2150

2150 + 86 = 2236

Same here. Simples !!

ExSp33db1rd

15th May 2013, 04:32

How quickly can you still add up:

7/6

4/5

6/3

1/11

3/2

failed - I said 23/3d

West Coast

15th May 2013, 06:01

Can I multiply 42 and 53 in my head?

Easily, don't get the right answer though.

Tankertrashnav

15th May 2013, 08:27

Tankertrash - £1-3-3d is correct - you're hired!

Norman - for a while after I retired I had a part time job in the filling station down the road. The till scanned the items for price, totalled it then told you what change to give for the amount tendered. In spite of that I couldnt stop myself doing a running check of the total in my head and checking that it was telling me to give the right change!

If you ever want to confuse a young till operator, offer them the odd 7p when they've already rung your £10 through for your £8.07 purchase (for example). The consternation can be pitiful!

The SSK

15th May 2013, 08:31

I can remember how to work out square roots (of anything, to umpteen decimal places) with pen & paper, using a method very similar to long division.

At least I could, last time I tried.

Just off to try it on 2236 ...

Fareastdriver

15th May 2013, 11:02

How quickly can you still add up:

7/6

4/5

6/3

1/11

3/2

I failed too. I got 1 guinea 2s 3d'

rgbrock1

15th May 2013, 11:40

I'm lucky I can multiply 2x2 in my head. One of the pluses of sitting in front of a computer all day.

funfly

15th May 2013, 11:56

Can I multiply 42 and 53 in my head?

Step 1: 3 x 2 = 6

Step 2: (3 x 4) + (5 x 2) = 22

Step 3: 5 x 4 = 20

Step 5: take step 3, 20 add step 2 to get 222 then add step 1 to get 2226

As per our Indian friend.

Must watch the video again to get it in my brain though:ugh:

MagnusP

15th May 2013, 12:56

Well, if you convert them to binary, 43 AND 52 is 32.

rgbrock1

15th May 2013, 13:06

MagnusP wrote:

Well, if you convert them to binary, 43 AND 52 is 32.Geek. Do you have a binary wristwatch as well? :}:}:}

MagnusP

15th May 2013, 13:13

Geek.

Guilty as charged, m'lud. :O

teeteringhead

15th May 2013, 13:21

funfly

except it's 2236! The way I learnt the Vedic method - many years ago - was something like this:

2 x 3 = 6 ...... so 6 is last place

then "crosswise" multiplication

(4 x 2) + (3 x5) = 23 ..... so 3 is in next place - and carry the 2 to the left

4 x 5 =20 add the 2 you carried is 22 for leading places answer is 2236.

Helps - well helps me - to imagine the numbers written one above the other with a big X showing the "crosswise" bit.

Indeed, there is a theory that says that is where the X for multiplication originated....

With practice you can write the number (right to left) pretty much as fast as someone calls out the numbers.

Or do squaring of 2-digit numbers using the same system. It seems harder but is in fact easier/quicker than using different numbers. And I have won beer doing it!!

rgbrock1

15th May 2013, 13:44

teeteringhead:

Thanks for that. As I attempted to wrap my brain around your explanation, it exploded. There's just a slight wisp of smoke left.

spInY nORmAn

15th May 2013, 18:37

If you ever want to confuse a young till operator, offer them the odd 7p when they've already rung your £10 through for your £8.07 purchase (for example). The consternation can be pitiful!

I do this regularly and chuckle to myself as the (usually young) cashier stands there slack jawed looking at the register as if it's going to provide the answer. After a brief pause I will tell them how much change to give me much to their relief (I'm sure I could tell them any amount at that point and they'd believe me!).

By the way, the Board of Examiners have determined that 23/3 and 1 guinea 2/3 are acceptable answers :ok:

rgbrock1

15th May 2013, 19:03

Hey, I did an experiment. I multiplied 10 x 10 and got the right answer! Yahooooooo.

probes

15th May 2013, 19:20

The way I was taught was to do 43x5, stick a 0 on the end & add 43x2 - mind you that was in about 1955 ! http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif

:sad: - lost art, sadly.

Can I? No, of course not. Unless I really have to.

Then I'd visualise it somehow, as usual.

ExSp33db1rd

15th May 2013, 20:20

I just put it on the little circular slide rule that I have glued inside the cover of my wallet - to confuse the check-out operators, who can't even pronounce 'slide rule', never mind know what it is, and definitely can't use one.

'course, one has to consider the decimal point - and accept an answer to the nearest 10 initially, but it's good enough to prove that the Barstewards are cheating me over the price of the "Super" size, "Cheap", offer for todays' "Special".

Such Fun !

moosp

15th May 2013, 20:38

At flying college back in the late 1960s we had an hour a day lecture on "Mental Calculations". The stuff we were able to do after three months still amazes me, and to see the calculations that the lecturer could approximate then refine were astounding.

It was probably the most rewarding subject that I ever studied, as it showed what a the human mind is capable of. I am very rusty now, but I did the above 43x52 as an approximation, which in aviation is usually close enough, by making it 45x50 = 2250 and deducting a third of the lower multiplier 45/3 =15 = 2235.