OT: Mathematical Conundrum II

[Syd Rumpo]

6 + e^(i*pi) pence.

Cheers

[Cursitor Doom]

Stay tuned. They'll get progressively trickier. :->

[Cursitor Doom]

FINALLY! The correct answer. ;-)

[Johnny B Good]

That smacks of the iteration process used to calculate a square root. If you're going to use this method here, you'd "split the difference" and make your next "guess" 5p and try again, arriving at the correct answer in only two "guesses" as opposed to the six guesses implied by your method. :-)

You'd have to be pretty innumerate to not be able to "Guess and Test" your way to the correct answer. :-)

[NY]

It's the "in your head" bit that stumps me. I did it in about 10 seconds with by adding two simultaneous equations to eliminate one of the two variables and hence give a value for the other one. But I needed it to write it down to see the equations in front of me. It's the same with arithmetic. I can do any calculation as long as I have a pen and paper, but I need to write it down because I can't visualise the units, tens, hundreds columns and the carry digits as I add up each of them in turn.

I've always admired people who can do mental arithmetic and can keep a running total as they add a series of multi-digit numbers together: without the ability to see what I'm doing as I go along, I'm utterly lost.

I think it's because I've never been able to do (for example) 15+27 as a single calculation, but as and iterative process: "5 and 7 is 12: write down

2 in units and carry 1 to tens; 1 and 2 and (carried) 1 is 4 - answer 42".

[Jim_S]

So he's right!

[News]

In message , Cursitor Doom writes

Three men go to a pub for a meal. Total bill is thirty pounds so they each put in a tenner. Waitress realises bill should only be 25 pounds so, not being able to divide 5 by three, she gives the men one pound each and pockets two pounds.

The three men have paid (3x9) 27 pounds, the waitress has pocketed 2 pounds - where is the other pound?

[Albert Zweistein]

Couldn't you mentally break 15+27 into 27+10+5 thus giving you the easily calculable intermediate stage of 37+5 and the easy final answer of 42 ?

[Adrian]

It doesn't exist, because your wording is deliberately intended to misdirect.

They put £30 on the table. She returned £3, leaving £27 on the table. She took £2, leaving £25 on the table. The wording suggests that her £2 came out of that £3, leaving the missing £1.

[Adrian]

Or, even quicker and easier, 15 + 30 = 45 - 3 = 42.

[Albert Zweistein]

Clever the way phraseology can mask the truth. £25 for actual bill (£30 - £5), £3 for men (£1 each), £2 for opportunist waitress. £25 + £3 + £2 = £30

[Chris Hogg]

UR Deep Thought AICMFP!

[Albert Zweistein]

Actually thinking about it both our suggestions involve retaining an intermediate answer in the mind which is then operated on once more, no doubt we both find that easy but the OP said he can't do that. Different people have different capabilities.

[NY]

Either of these methods is dead easy when you can see the equations before your eyes. Trying to do it "blind" without writing down what you are doing is where I seem to have a complete mental block.

[Albert Zweistein]

Yeah I get it, I can't whistle in tune because of a mental block. I'm pretty good at mental arithmetic but I'd rather be able to whistle.

[Cursitor Doom]

Same here! I also struggle sometimes with the initial process of formulating the original real-world problem into an equation (or equations). Only once I'm into the pure math realm do I feel at home.

[GB]

Fortunately, there's usually a pin to prevent activation in these circumstances.

[Albert Zweistein]

Yes damn clever that, the way that the wording makes it seem that 30 has to be part of the final equation and neglects to mention the pubs slice of the pie at all (which is critical) yet seems at first sight to be a logical argument. So we end up with:- men (3 * -9) = -27 and [pub (+25) + waitress (+2)] = +27. so it's +27 and -27 that balance out with not a 30 to be seen. This is quite trivial but cunningly hidden in the words of the original posting which could be rephrased as a man walked into a pub with 27 units and gave the pub 25 units and the waitress 2 units. I'm waiting for my dinner to finish cooking. Can you tell?

[dennis]

Its 5d and £1 5d. Pence are old money so there are 12 pence in a shilling so its not a shilling..

[pamela]

That's a good one. I like it. :-)