[Finance] Maths Tips and Tricks

[Brightonfan1983]

Listening to "More or Less" just now, they presented the little-known (apparently) fact that any percentage of any amount is the same the other way around, ie. 4% of 75 is the same as 75% of 4 = 3. Which I think is very cool.

Then, there's the 9x table on your fingers: with your hands out in front of you, 3x9 = drop your 3rd finger on the left, you now have 2 fingers to the left of it, and 7 on the right, so your answer is 27.

I've always like coping with dividing fractions (not a daily need, I grant you, but still): 1/3 divided by 2/5 = 1/3 x 5/2 = 5/6.

Anyone else have some trivia/shortcuts they can share?

 

[pasty]

If all the digits of a number add up to something that is divisible by 3, then that number is divisible by 3

Only ever found that useful in the numbers round on Countdown

 

[JimothyJames95]

I know for Trigonometry, when figuring out angles and lengths if you use SOH CAH TOA for the various sides of the triangle in relation to the angle. So if you use S = Sine and put the Opposite (O) over the Hypotenuse (H). Works for the other ones as well. Helped me when I was at school for my GCSE’s and with my job doing drawings for some certain designs for unknown lengths which were unable to be measured.


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[Is it PotG?]

The Abbott formula always works for me

 

[Justice]

iPhone Calculator work for me

 

[Brightonfan1983]

The Abbott formula always works for me

OK I'll bite... What is that?

 

[Brightonfan1983]

If all the digits of a number add up to something that is divisible by 3, then that number is divisible by 3

Only ever found that useful in the numbers round on Countdown

Oh that's good. On a recent Fish podcast, they were discussing prime numbers. They are searched for now with the formula (2x2x2....)-1. Each result can also be written as 1111.... in binary. Mental.

*Not that you were talking about prime numbers, it just reminded me...

 

[Is it PotG?]

OK I'll bite... What is that?

 

[JimothyJames95]

This trick works quite well.

https://youtu.be/dXbHaOradg4


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[Nottseagull]

Listening to "More or Less" just now, they presented the little-known (apparently) fact that any percentage of any amount is the same the other way around, ie. 4% of 75 is the same as 75% of 4 = 3. Which I think is very cool.

Then, there's the 9x table on your fingers: with your hands out in front of you, 3x9 = drop your 3rd finger on the left, you now have 2 fingers to the left of it, and 7 on the right, so your answer is 27.

I've always like coping with dividing fractions (not a daily need, I grant you, but still): 1/3 divided by 2/5 = 1/3 x 5/2 = 5/6.

Anyone else have some trivia/shortcuts they can share?

I had an excellent Primary School education at West Hove where we did long division etc but I wasn't taught any of those methods at any school. Is this the same for anybody else?

 

[Brightonfan1983]

Very basic, but if you want to multiply a number by 5, it's easier to halve it then multiply it by 10.

eg. 1038 x 5

1038 / 2 = 519

519 x 10 = 5190

So basic that I bet not that many people know it as an easy shortcut.

I work as a supply teacher occasionally and I can guarantee you, the easiest ways in maths are never taught. I shall use that deffo

 

[Coldeanseagull]

OK I'll bite... What is that?

It's a brand of powdered milk......or something to do with pesticide

 

[timbha]

If the digits of a number add up to a number divisible by 9, then the original number is divisible by 9
Eg
27 = 2+7 = 9
Or
999 =9+9+9=27=2+7=9

 

[Nottseagull]

If the digits of a number add up to a number divisible by 9, then the original number is divisible by 9
Eg
27 = 2+7 = 9
Or
999 =9+9+9=27=2+7=9

I was taught that only work for 3!

 

[studio150]

So basic that I bet not that many people know it as an easy shortcut.

I work as a supply teacher occasionally and I can guarantee you, the easiest ways in maths are never taught. I shall use that deffo

Really depends on how good you are at mental arithmetic, but to me just seems like an unnecessary extra step when multiplying by 5 which is straightforward.

No doubt most today would just reach for a calculator

 

[Nottseagull]

So basic that I bet not that many people know it as an easy shortcut.

I think the opposite, i.e. it's something most people would easily have thought of themselves - not just 10, but splitting any calculation into much simpler ones then adding the results together.

 

[Nottseagull]

Really depends on how good you are at mental arithmetic, but to me just seems like an unnecessary extra step when multiplying by 5 which is straightforward.

Unless you are Rainman, you don't know your 1038 times table so I put it to you that you are only capable of working that out in your head by splitting it, probably as (5x1000)+(5x38).

 

[Nottseagull]

Are there any tips for subtractions?

You can back Cardiff to go down at 1.04 at Betfair, which equates to them having a 4.85% (100 - 96.15%) chance of staying up right now.

 

[Creaky]

The only ‘tip’ that I have used in practice is the 3 4 5 triangle.

A triangle with sides of 3 units, 4 units and 5 units has a right angle between the 3 and 4 sides.

Useful when wanting to layout a right angle for landscaping etc.

 

[Nigella's Cream Pie]

Are there any tips for subtractions?

Reverse addition, I always use in situation e.g. 345 - 67: I know that you need to add 33 to 67 to make 100, so add 33 to both to get 378 - 100 = 278