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Quiet Guy

Mental Arithmetic

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Are you ay good at mental arithmetic? What is 7 to the power of 4?

OK, that was a warm up. Now, what is 77 top the power of 17 in five seconds please.

http://www.wimp.com/germansuperbrain/

7 to the power of 4 is much easier than it first appears. 7*7*7*7=49*49=(50-1)*(50-1)=2500-100+1=2401.

I find it much easier to work with close round numbers than take the calculation head on.

The second question would take me until Doomsday.

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7^4 in under 30 seconds, but the other I could not do.

My mental arithmetic has always been pretty good. Dipped in my late teens, and then improved again working in the meat factory/warehouse. The math skills of the people working there (for minimum wage through an agency) was very good indeed. I took to shouting numbers for 'picks' in German when working with multiple Eastern Europeans of different tongues as they seemed to find it easier than English.

Half of the reason our team was the most efficient, was that we could plan picks very far in advance in our heads and make our workload much easier, so whilst we had the most breaks, we picked to a higher accuracy a greater amount of orders.

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7 to the power of 4 is much easier than it first appears. 7*7*7*7=49*49=(50-1)*(50-1)=2500-100+1=2401.

I find it much easier to work with close round numbers than take the calculation head on.

The second question would take me until Doomsday.

That's how I did it for case 1, I assume you have knowledge of factorisation. So easy for anyone with A-level maths.

77^17 seems much harder , not sure what tricks might help.

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That's how I did it for case 1, I assume you have knowledge of factorisation. So easy for anyone with A-level maths.

Or less. I knew the answer anyway, but would probably have used difference of two squares thus: 49 x 49 = (50 x 48) + 1 .

77^17 seems much harder , not sure what tricks might help.

Indeed it would be fascinating to hear from the guy himself how he did/does it.

Also is it significant to note that in all five of the tests, the exponent was never greater than 20? Does this mean that the chap can't work with higher values? And if so... what if he'd simply memorised all the powers up to 20 of all two-digit numbers? That would still mean tens of thousands of digits to swot up, but even such a prodigious achievement would be small compared to the astonishing claim of actually calculating each and every one of them from scratch, reciting them immediately, rapidly and without hesitation.

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Don't know about this man but possibly an 'Idiot Savant'

I once knew someone who was obviously mentally subnormal yet could draw fantastically.

He told me that he could 'see' what he wanted to draw on a blank piece of paper and merely traced around it.

He found it difficult to understand that other people could not do this.

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I dunno, but astronauts in training, when asked to subtract 7 from 100 repeatedly (100, 93, 86...) whilst having their blood pressures measured, scored 245 / 140!

http://www.spacedoc.com/blood_pressure_personality_heart_attack_risk

The OP test has a degree of difficulty, taking 7 off backwards is almost as instantaneous as counting forward 1,2,3,4.....so I am surprised that astronauts would stress over this test as the speed element would be marginal for somebody reasonably numerate.

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  • 244 Brexit, House prices and Summer 2020

    1. 1. Including the effects Brexit, where do you think average UK house prices will be relative to now in June 2020?


      • down 5% +
      • down 2.5%
      • Even
      • up 2.5%
      • up 5%



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