Scientific Calculator

[Edwards]

I was careful to use a solid object in my example one that has a mass.

Not a theoretical example thus it does not need any extra twiddly bits.

For those that claim I am wrong I am waiting for my 2 pounds.

[TonyR]

For those that claim I am wrong I am waiting for my 2 pounds.

Do you want your 2 pounds in rocks or feathers? Or have you unintentionally promulgated another ambiguity?

[Edwards]

For those that claim I am wrong I am waiting for my 2 pounds.

Do you want your 2 pounds in rocks or feathers? Or have you unintentionally promulgated another ambiguity?

Either and it was intentional to add some humour.

[Psamathe]

I remember quite a few years ago opening a savings account (in the days when you went into a branch ...). And the interest rate was (can't remember but say) e.g. 5%. So I ask "Interest calculated on the account balance ?" Answer "Yes it is". So "How often is the interest calculated and added to the account ?" And the banker answers "As often as you want". Me thinks that said banker does not understand "compound interest". So I did try the "every microsecond" answer and can't remember the ensuing discussion but I did enjoy explaining something as basic as compound interest to a banker.

Ian

[Mick F]

One good thing about arithmetic is as it's the study and manipulation of numbers, so it can be used for apples and oranges etc.

You don't need an appreciation of Messers Bodmas and Bidmas to know full well that 1 + 2 x 3 = 9 when you're discussing fruit or pound coins.

It's only when you look at numbers and operations in isolation that you need mathematical rules, because common sense will prevail with fruit or pound coins.

[Mick F]

PS
Compound interest.
This is a good diagram from Wiki.

[Edwards]

I tried to show that there is a convention in the use of language in relation to maffs. If using a different counting system then you need to say you are doing so.

Pleased to note at least one person thought I was asking for money as I recall saying send me 2 pounds.
When asked about rocks or feathers I could have replied Diamond encrusted rocks or best Eider Duck Down. But lets not be greedy.

[Psamathe]

Go to market stall with an offer of 20% off

Shopping bill becomes 1.26 + 3.80 + 2.97 + 0.67 x 0.8 (0.8 for the 20%off)

Should I be taking my Windows or Mac calculator with me ?

Ian

[Mick F]

Neither.
Use a bit of paper and a pen, or do it in your head. I'd need paper and pen!

20% off is one fifth.
Shift the decimal point one to the left and double the result.
Take that figure off the original total.

ie
1.26 + 3.80 + 2.97 + 0.67 = £8.70

10% is 87p
20% is £1.74
£8.70 minus £1.74 = £6.96

[Psamathe]

Neither.
Use a bit of paper and a pen, or do it in your head. I'd need paper and pen! :oops:

20% off is one fifth.
Shift the decimal point one to the left and double the result.
Take that figure off the original total.

ie
1.26 + 3.80 + 2.97 + 0.67 = £8.70

10% is 87p
20% is £1.74
£8.70 minus £1.74 = £6.96

I mean, should the calculation be
1.26 + 3.80 + 2.97 + 0.67 x 0.8 i.e. 1.26 + 3.80 + 2.97 + (0.67 x 0.8)

or should it be:
(1.26 + 3.80 + 2.97 + 0.67) x 0.8

because 1.26 + 3.80 + 2.97 + 0.67 x 0.8 or 1.26 + 3.80 + 2.97 + (0.67 x 0.8) would be the "proper way" to evaluate it according to some (and the more expensive way).

And according to previous posts, entering 1.26 + 3.80 + 2.97 + 0.67 x 0.8 into Windows Calculator and OS X Calculator would give different answers.

Ian

[IanW]

Go to market stall with an offer of 20% off

Shopping bill becomes 1.26 + 3.80 + 2.97 + 0.67 x 0.8 (0.8 for the 20%off)

Should I be taking my Windows or Mac calculator with me ?

Ian

Under MickF's maffs (which is the term I am going to use for the abandonment of BODMAS) MickF's shopping bill would be £6.96

But under my "maths" my shopping bill would appear to be £8.56[6]

So under these circumstances I think I prefer MickF's maffs.

But hang-on I'll go for maths' distributive law, so, it's: 1.26 x 0.8 + 3.8 x 0.8 + 2.97 x 0.8 + 0.67 x 0.8 which equals £6.96 again.

Phew, that was close, Mick nearly undermined my entire maths education

[Mick F]

My basic cheapo calculator says 1.26 + 3.80 + 2.97 + 0.67 x 0.8 = 6.96 ...... which is correct for the market produce.
My Mac scientific calculator says 1.26 + 3.80 + 2.97 + 0.67 x 0.8 = 8.566 ............ which is correct mathematically but incorrect at the market.

Perhaps it should be (1.26 + 3.80 + 2.97 + 0.67) = 8.70 x 20/100 = 1.74(M+) 8.70 - MR = 6.96
Doing it that way, both calculators are correct.

[sjs]

For even more fun and enjoyment we could introduce Excel and its various imitators into the discussion. Where (for instance) -2^2+1 is not the same as 1-2^2. BODMAS does not address unary minus signs.

[freeflow]

I'd be horrified if they were the same. That second expression should be 1- -2^2 to be the same as the first expression.

[sjs]

Eh? According to Excel -2^2 is 4, ie (-2)^2. That doesn't feel right to me. On the other hand 1-2^2 is -3 (different kind of -), and I guess 1- -2^2 would also be -3, though maybe just gives an error. In the programming languages I know -2^2+1 would be the same as +1-2^2, probably including visual basic.