- posted on March 27, 2016, 8:57 pm

Is 987659387043185671335 divisible by 9? Add up each digit: 9+8+7+6+5+9+3+8+7+0+4+3+1+8+5+6+7+1+3+3+5 = 108 Add up each digit of that: 1+0+8 = 9. 9 is divisible by 9, so so is 987659387043185671335.

If you can give me a reason why this works, you're cleverer than I am.

- posted on March 27, 2016, 9:07 pm

Yes, here is the result

1.097399319×10²⁰

- posted on March 27, 2016, 9:16 pm

If you do it my way you don't need a calculator.

-- "Okay, okay, I take it back! UnFuck you!"

- posted on March 27, 2016, 10:13 pm

On 03/27/2016 04:16 PM, Mr Macaw wrote:

Sheesh...I worked with a guy who could probably not calculate anything more difficult than 2 x 2 = 4 unless he used a calculator

Sheesh...I worked with a guy who could probably not calculate anything more difficult than 2 x 2 = 4 unless he used a calculator

- posted on March 27, 2016, 11:00 pm

Is that in merca?

-- 5 Brits were injured last year in accidents involving out of control Scalextric cars.

- posted on March 28, 2016, 12:03 am

On 03/27/2016 06:00 PM, Mr Macaw wrote:

Hugh betcha

Hugh betcha

- posted on March 27, 2016, 10:16 pm

On Sunday, March 27, 2016 at 5:07:38 PM UTC-4, philo wrote:

I presume he really means evenly divisible.

I presume he really means evenly divisible.

- posted on March 27, 2016, 11:02 pm

That's what divisible means.

-- Acupuncture is a jab well done.

- posted on March 28, 2016, 12:12 am

That's what divisible means.

-------------

no.

- posted on March 28, 2016, 12:17 am

rote:

Yes. If someone says "12 is divisible by 4", they mean "to produce a whole number". If someone said "13 is divisible by 4" they would be incorrect.

-- If you own a 3,000 machine gun and a 5,000 rocket launcher, but you can't afford shoes, you may be a Muslim.

- posted on March 28, 2016, 12:34 am

Yes. If someone says "12 is divisible by 4", they mean "to produce a whole number". If someone said "13 is divisible by 4" they would be incorrect.

-----------

no.

https://en.wiktionary.org/wiki/evenly_divisible

http://www.mathwarehouse.com/dictionary/D-words/definition-of-divisible.php

--------------------

"You just reminded me why my pure maths course at uni made me wish I was in engineering class."

----------------

Indeed. But engineering classes understood what is meant by "evenly divisible" too. It is a pretty basic concept. Like 3rd grade?

--

If you own a ?3,000 machine gun and a ?5,000 rocket launcher, but you can't

afford shoes, you may be a Muslim.

If you own a ?3,000 machine gun and a ?5,000 rocket launcher, but you can't

afford shoes, you may be a Muslim.

Click to see the full signature.

- posted on March 28, 2016, 8:24 pm

On Sunday, March 27, 2016 at 8:34:40 PM UTC-4, taxed and spent wrote:

le

hp

Your two references contradict each other. One says that just divisible means it has to be evenly divisible, ie with no remainder. That seems to be the correct definition, multiple source confirm it. So saying evenly divisible is not needed, it's already implied.

le

hp

Your two references contradict each other. One says that just divisible means it has to be evenly divisible, ie with no remainder. That seems to be the correct definition, multiple source confirm it. So saying evenly divisible is not needed, it's already implied.

- posted on March 28, 2016, 8:43 pm

whole

ct.

e.php

as in

Not required in more advanced engineering.

-- "Get as far away from the nuclear explosion as possible" - Rodney McKay, Stargate Atlantis.

- posted on March 27, 2016, 10:35 pm

I'll illustrate the principle using a 3-digit number. Pick any three digits, and designate them as a, b, and c.

The sum of the digits is a + b + c; call this s. The value of the number is (100

The difference between the value of the number, and the sum of its digits, is v - s = (100a + 10b + c) - (a + b + c) = 99a - 9b = 9(11a - b)

Therefore, (v - s) must be a multiple of 9 (and hence of 3 also).

If s is a multiple of 3, and you add a multiple of 3 to it, the result must also be a multiple of 3, and likewise for multiples of 9.

Therefore if s is a multiple of 3 (or 9) then v = s + (v - s) is also a multiple of 3 (or 9).

For a four-digit number abcd, (v - s) = 999a + 99b + 9c = 9(111a + 11b + c) which is clearly a multiple of 9. And so on, for numbers having 5, 6, 7, etc. digits.

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