Factorial seconds

How many weeks are there in 10 ! 10! seconds?

(Please note the factorial sign)

Image credit: Wikipedia Ancheta Wis


The answer is 6.

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19 solutions

Chew-Seong Cheong
Sep 19, 2014

The number of weeks in 10 ! 10! seconds =

10 ! 60 × 60 × 24 × 7 = 2 8 × 3 4 × 5 2 × 7 2 7 × 3 3 × 5 2 × 7 = 2 × 3 = 6 \dfrac {10!} {60 \ \times 60 \times 24 \times 7} = \dfrac { 2^8 \times 3^4 \times 5^2 \times7 } {2^7 \times 3^3 \times 5^2 \times 7 } = 2 \times 3 = \boxed{6}

how did you convert the given factorial in powers directly?? pls answer..@!

Shivam Rana - 6 years, 8 months ago

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@Chew-Seong Cheong Yes how did you convert the factorial in powers?

U Z - 6 years, 7 months ago

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Sorry, I didn't read Shivam Rana's post earlier.

We note that 10 ! = 10 × 9 × × 8...1 10! = 10\times 9\times \times 8...1 . The prime factors involved are: 2 , 3 , 5 , 2,3,5, and 7 7 .

The power of 2 2 are given by 2 , 4 , 6 , 8 , 10 2 1 + 2 + 1 + 3 + 1 = 2 8 2,4,6,8,10 \Rightarrow 2^{1+2+1+3+1} = 2^8

Similarly,

3 : 3 , 6 , 9 3 1 + 1 + 2 = 3 4 3: 3,6,9\Rightarrow 3^{1+1+2} = 3^4

5 : 5 , 10 5 1 + 1 = 5 2 5: 5, 10 \Rightarrow 5^{1+1} = 5^2

7 : 7 7 1 7: 7\Rightarrow 7^1

Therefore, 10 ! = 2 8 3 4 5 2 7 10! = 2^83^45^27

Chew-Seong Cheong - 6 years, 7 months ago

It wasn't directly, he/she skipped a step or two.

Alex Bean - 6 years, 8 months ago

using scientific calculator

Mohammed Ismail - 6 years, 8 months ago

10!sec = 3628800 sec = 1008 Hrs = 42 Day = 6 weeks

Mohammed Ismail - 6 years, 8 months ago

That ! sign is hard -.-

Peter Alvin Arante - 6 years, 8 months ago

Factorial conversion please

Viju Raj - 6 years, 7 months ago

hahahaha i forgot minutes.. :D

Shah Jahan S J - 6 years, 7 months ago

good solution! i too used this way

Shourya Gupta - 6 years, 7 months ago

A nyc one!!

Sai Krishna Dittakavi - 6 years, 8 months ago

a different one !

RLibra Khan - 6 years, 8 months ago

How can there be 6 weeks in just 10 seconds? I don't get it.

Claire Kesterke - 6 years, 8 months ago

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everyone else seems to have actually calculated the factorial

my light calculation version:

10!=10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 seconds

1min=60sec= 10 * 6sec

so 9 * 8 * 7 * 5 * 4 * 3 * 2 minutes

1hr=60 min=3 * 4 * 5 min

so 9 * 8 * 7 * 2 hours

1day=24hr=8 * (9/3) (I pulled the three for this out of the nine)

so 3 * 7 * 2 days

1week=7 days

so 3 * 2 weeks

didn't feel like pulling up a calculator and was too tired to think of big numbers. sorry about the formatting, had a little trouble with brilliant's editor. which seems odd to me, because I've been using latex for years.

Keegan Lee - 6 years, 7 months ago

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i did the same, it took 5 min to do it without pen and paper though

Dilip Kumar - 6 years, 7 months ago

Its not 10 10 seconds but 10 ! 10! seconds which is equal to 3628800 3628800 seconds. @Claire Kesterke

Harsh Shrivastava - 6 years, 8 months ago

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Oh okay, thanks I missed the !

Claire Kesterke - 6 years, 8 months ago

Its not seconds but 10! seconds which is equal to 3628800 seconds

Jiro Dy - 6 years, 8 months ago

its a factorial seconds ;)

Thumper Parnoncillon - 6 years, 8 months ago

Claire Kesterke - it isn't 10 seconds - it is 10! seconds - the ! sign is important means factorial (you multiply all the integers from 1 to n together) : 3 ! = 3 2 1 3! =3 * 2 * 1 4 ! = 4 3 2 1 4! = 4*3*2*1 so by extension 10 ! = 10 9 8 7 6 5 4 3 2 1 10! = 10*9*8*7*6*5*4*3*2*1

Tony Flury - 5 years, 9 months ago

10X9X8X7X6X5X4X3X2X1/ 60X60X24X7= 6 weeks

Now, one thing, important one, we often confuse the conversion.

so, try to do it like this: (10! seconds) X (1 minute/ 60 seconds) so that seconds cancels and we are left with minutes, so in this way, it will be easier!

Ankit Singhal - 6 years, 8 months ago
Rio Pradana
Sep 22, 2014

(10!)/week =(10!) / (days x hours x minutes x seconds) =(10!) / (7x24x60x60) =(10!) / [7x(3x8)x(3600)] =(10!) / [7x3x8x(4x9x10x2x5)] =(10x9x8x7x6x5x4x3x2x1) / (10x9x8x7x5x4x3x2) =6x1 = 6

best understanding

ALi Chohdry - 6 years, 8 months ago

Best Solution! ^^

Angel Nacino - 6 years, 8 months ago
Tarun Mali
Sep 18, 2014

10!÷7×24×60×60

how get 6...?

anees ani - 6 years, 8 months ago

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10! = 3628800 1Week = 7 24 60 60(7days in a week, 24 hrs a day, 60 min in a hr, 60sec in a minute) 3628800 \ (24 60 60 7) = 6

Abhishek Harit - 6 years, 8 months ago
Hobart Pao
Sep 21, 2014

I would use dimensional analysis 10! = (10 x 9 x 8 x 7 x 6 x 5 x 4 x 3 x 2) sec x (1 min)/(60 sec) gives 9 x 8 x 7 x 5 x 4 x 3 x 2 min (9 x 8 x 7 x 5 x 4 x 3 x 2 min) x (1 hr)/(60 min) gives 9 x 8 x 7 x 2 hrs (9 x 8 x 7 x 2) hrs x (1 day)/(24 hrs) gives (3 x 7 x 2) days (3 x 7 x 2) days x (1 week)/(7 days) gives 3 x 2 = 6

That really isn't dimensional analysis though - it is just division and cancelling factors.

Tony Flury - 5 years, 9 months ago

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In America where everything is dumbed down, it's called dimensional analysis. Our chemistry and physics classes have a whole unit dedicated to it.

Hobart Pao - 5 years, 9 months ago

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I would have thought dimensional analysis was more to do with when you combine different units together (say Force, distance & time) how that combination creates compound units or even new units (for instance power) - part of that is understanding conversion factors though - I accept that).

Tony Flury - 5 years, 9 months ago

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@Tony Flury lol some of the american dimensional analysis problems was converting weeks to seconds. very dumbed down

Hobart Pao - 5 years, 9 months ago
Somesh Singh
Sep 21, 2014

best way is to go on cutting terms from factorial 10...first off, 24 is fact.4 so 4x3x2x1 are gone from numerator, then cut 7...now we're left with 10 9 8 6 and 5 in numerator and 3600 in the denom....5x6=30 / 3600 = 1/120.... cut 10x9x8 by 120....answer is 6

Andrea Palma
Apr 19, 2015

one week in seconds is

7 (days in a week) x 24 (hours in a day) x 3600 (seconds in a hour)

so we have

7x(3x8)x(36x100) seconds in a week.

Using a comfortable factorization . 36 = 9x4 and 100 = 2x5x10 so the seconds are

7x3x8x9x4x2x5x10 = (ordering by growing factors) = 2x3x4x5x7x8x9x1x0 = (10!)/6

And trivially the answer is 6 without any calculation,

Jack Saraceno
Nov 19, 2014

compute what 10! = 3628800. Then there are 60 seconds in 1 minute and 60 minutes in 1 hour and 24 hours in 1 day. To get how many seconds in 1 day multiply 60 seconds times 60 minutes times 24 hours to get 86400. Then divide 10! by 86400 to get 42, then there are 7 days in a week divide 42 by 7 to get 6.

10!/7/24/60/60=6

Connor Carr
Oct 28, 2014

I just did something easy. Figured out what 10! was on a Google calculator, then divided by 60 to change from seconds to minutes, divide by 60 again to change from minutes to hours, divide by 24 to change from hours to days, then divide by 7 to change days to weeks. It's what everyone's saying, but doing it all 1 at a time makes it a little easier to follow.

10 9 8 7 6 5 4 3 2 7 4 6 6 10 6 10 = 10 5 2 10 10 9 8 3 6 6 6 7 4 7 4 6 = 6 \frac { 10\cdot 9\cdot 8\cdot 7\cdot 6\cdot 5\cdot 4\cdot 3\cdot 2 }{ 7\cdot 4\cdot 6\cdot 6\cdot 10\cdot 6\cdot 10 } =\frac { 10\cdot 5\cdot 2 }{ 10\cdot 10 } \cdot \frac { 9\cdot 8\cdot 3 }{ 6\cdot 6\cdot 6 } \cdot \frac { 7\cdot 4 }{ 7\cdot 4 } \cdot 6=6

Factorization works: Ensuring units cancel

Number of weeks = (10! secs) * (1 min/60sec) * (1 hrs/60min) * (1 day/24hrs) * (1weeks/7 day) = (10! weeks) / ( 60 * 60 * 24 * 7) = (10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 weeks) / ((10 * 6)(5 * 4 * 3)(8 * 3)(7))

Rearrange in descending order for clarity: = (10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 weeks) / (10 * 8 * 7 * 6 * 5 * 4 * 3 * 3)

Cancelling common factors = (9*2 weeks) / (3) = 6 weeks ===>

Shouvik Roy
Oct 19, 2014

10 9 8 7 6 5 4 3 2 1 =[ 7 (6 10) (5 4 3) (8 3)] 3 2 which leaves 6.

Alex Bean
Oct 13, 2014

We first note that 10 ! s e c o n d s 10! seconds is equal to

10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 seconds.

The 1 changes nothing and can be removed to get

10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 seconds.

To change seconds to minutes, we divide by 60 60 . This cancels with the 6 6 and 10 10 , so we have

9 × 8 × 7 × 5 × 4 × 3 × 2 9 \times 8 \times 7 \times 5 \times 4 \times 3 \times 2 minutes.

Now we need to change minutes to hours, for which we again divide by 60 60 . We can cancel this with the 5 5 , the 4 4 , and the 3 3 to get

9 × 8 × 7 × 2 9 \times 8 \times 7 \times 2 hours.

To change to days, we need to divide by 24 24 . We can cancel with the 8 8 and the 9 9 . We're dividing the 9 9 by 3 3 , as we don't have any other 3 3 s to cancel. This gives us

3 × 7 × 2 3 \times 7 \times 2 days.

Finally, we have to divide by 7 7 to get weeks, and we cancel to get

3 × 2 3 \times 2 weeks.

This simplifies to our final answer of

6 \boxed{6} weeks.

Ken Bermudez
Sep 30, 2014

(1x2x3x4x5x6x7x8x9x10)/(60x60x24x7) = 6

Dladla Arthur
Sep 25, 2014

10! seconds = 10 9 8 7 6 5 4 3 2*1 = 3628800 seconds.

Seconds in a week:

3600 second in an hour.

3600*24 h = 86400 seconds in a day.

86400 * 7 days a week = 604800 seconds in a week.

therefore : 3628800/604800 = 6 weeks.

Olivia Ross
Sep 21, 2014

We had to memorize factorials up to 10 in class for homework:

3! = 6

4! = 24

Knowing these of the tops of our heads, we can use them to limit the amount of work needed to be done.

10 ! 3 ! 10 3 ! 10 4 ! 7 \frac{10!}{3! * 10 * 3! * 10 *4! *7}

This is to convert seconds to weeks. 60 is also equal to 3! * 10, so divide it by this twice to get minutes, then hours. We know 4! is 24, so dividing this way will get us the number of days. Then, divide by 7 to get weeks. Lastly, because dividing by a, b and c is the same as dividing by the product of a, b and c, we can multiply them all and divide, rather than dividing in several steps.

= 10 9 8 7 6 5 4 3 2 1 3 2 1 10 3 2 1 10 4 3 2 1 7 \frac{10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1}{3 *2 * 1 * 10 * 3 * 2 * 1 * 10 * 4 * 3 * 2 * 1 * 7}

After this, we can easily simplify, leaving us with only 6 in the numerator and three ones in the denominator.

Afnan Ali
Sep 21, 2014

easy way!!! 60/10=6>>>>>>>>60 min and 10 sec converting it we get 6 its EASy

Ramsha Ijaz
Sep 21, 2014

1minute=60seconds 60480minutes=10!seconds

1hour=60minutes 1008hours=60480minutes

1day=24hours 42days=1008hours

1week=7days 6weeks=42days

10!÷7×24×60×60 =7

\frac {10! s}{1 wk \times 7 \frac {days}{wk} \times 24 \frac {hrs}{day} \times 60 \frac {min}{hr} \times 60 \frac {s}{min}} = \frac {10 \times 9 \times 8!}{(7)(8 \3)(6\*5\*2\*1)(4\*15)) = (10\*9)/(15)*(8!)/(8\*7\*6\*5\*4\*3\*2\*1) = (90/15) \times (8!/8!) = 6 1 = 6

Ryan Bogner - 6 years, 8 months ago

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