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Algebra Level 1

999 9 999 999 9 998 999 9 998 = ? \frac{ 9999^{999}-9999^{998} } { 9999^{998} } = \ ?

9999 10000 1 9998

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30 solutions

Michael Fuller
Aug 22, 2015

9999 999 9999 998 9999 998 \large \dfrac{{9999}^{999}-{9999}^{998}}{{9999}^{998}}

= 9999 999 9999 998 9999 998 9999 998 \large=\dfrac{{9999}^{999}}{{9999}^{998}}-\dfrac{{9999}^{998}}{{9999}^{998}}

= 9999 1 = 9998 \large=9999-1=\color{#20A900}{ \boxed {9998}}

i think you has the easiest way to solve this problem without writing

Lê Triết - 5 years, 9 months ago

I forgot! there's 1 also. hehe, I just solved it mentally and I forgot that there's still 1 in the equation.

Danrey Vallejos - 5 years, 9 months ago

nice and easiest way to solve

Hadia Qadir - 5 years, 9 months ago

We can make just like this: (9^9-9^8)/9^8 = 8. Take 999 and write 8 in the end.

Jack Black - 3 years, 5 months ago

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That’s just great.

Karen Siegemund - 3 years, 1 month ago

Best solution

Syed Zaidi - 5 years, 9 months ago

Gracias amigo

naveen naveen - 4 years, 4 months ago

999 9 999 999 9 998 999 9 998 \frac{9999^{999}-9999^{998}}{9999^{998}}

= 999 9 998 × ( 9999 1 ) 999 9 998 =\frac{9999^{998} \times(9999-1)}{9999^{998}}

= 999 9 998 × 9998 999 9 998 = 9998 1 = 9998 =\frac{9999^{998}\times9998}{9999^{998}}=\frac{9998}{1}=\boxed{\color{#D61F06}{9998}}

Your head won't blast. But your calculator totally will.

I find this to be the simplest solution which is how I answered it in my head.

Kamal Gilkes - 5 years, 9 months ago

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Well, anyone can do this, just poor for the computer.

Adam Phúc Nguyễn - 5 years, 9 months ago

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Tại sao lại chuyển 9999^998 thành 9998 vậy b?

Nhiên Lê - 5 years, 9 months ago

I did it like @Michael Fuller, but i really like this approach!

Stephen Ermshar - 5 years, 9 months ago

x^2 (x-1)= x^2(x) - x^2(1)= x^3 - x^2
That's distributive property. 9999^999 - 9999^988 = 9999^998 x (9999 - 1)= 9999^998 x (9999) - 9999^998 x (1) = 9999^999 - 9999^998

I probably made a mistake somewhere, but ... Distributive property. Not very intuitive here, but works.

@Jing Sheng you probably know the answer already but...

Ren Arsuv - 4 years, 4 months ago

i don't understand step2. plz do more explanation Thankz. :)

Elipzid Zukkaraduss - 5 years, 9 months ago

I didn't answer step two too, someone please explain?

Jing Sheng - 4 years, 6 months ago

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I didn't understand*

Jing Sheng - 4 years, 6 months ago
Abrar Faiyaz
Aug 22, 2015

999 9 999 999 9 998 999 9 998 \frac{9999^{999}-9999^{998}} { 9999^{998}}

= 999 9 998 × ( 9999 1 ) 999 9 998 = \frac{9999^{998} \times (9999-1)} {9999^{998}}

The ' 999 9 998 9999^{998} ' cancels out to give ( 9999 1 ) = 9998 (9999-1) = 9998

I got the canceling out part but where does the 1 come from? (I would have picked 9999^999 to be the answer but it wasn't an option)

Andrew Ligon - 4 years, 9 months ago
Ezequiel Lopez
Aug 26, 2015

It's easy all of them have the same base so you can subtract the exponents in a division, so the first term of the subtraction after distribuying the division, is 9999^1 and the second term is just 1 so 9999 - 1 = 9998

That was how I solved it. It spared a lot of extra and unnecessary work.

Elizabeth Morley - 5 years, 9 months ago
Sam Tumlad
Aug 23, 2015

The same as X raised to the power of n. You first take out the LCD of the two terms on the numerator And then you cancel the factors. Then you are left with 9999-1. The answer is 9998.

Navu Katz
Aug 21, 2015

999 9 999 999 9 998 999 9 998 = 999 9 998 × ( 9999 1 ) 999 9 998 = 9999 1 = 9998 \frac{9999^{999}-9999^{998}}{9999^{998}} = \frac{9999^{998} \times (9999 - 1)}{9999^{998}} = 9999-1 = 9998

Lance Fernando
Aug 22, 2015

Using the DoTS property gives us 9999^998(9999 - 1) - cancelling the 9999^998. It remains like 9999 - 1, giving us 9998.

John Williamson
Aug 13, 2017

In my mind, I did a similar method to what many people below have described

Let A = 9999^998

(9999)A - A

= --------------- A

A (9999 - 1)

= --------------- A

= 9999 - 1

= 9998

Emerson Gomes
May 28, 2017
  • 999 9 999 999 9 998 999 9 998 \frac{9999^{999}-9999^{998}}{9999^{998}}

  • 999 9 998 ( 9999 1 ) 999 9 998 \frac{9999^{998}*(9999-1)}{9999^{998}}

  • 9999-1

  • 9998

Steven Mortensen
Apr 1, 2017

a n a n 1 = ( a 1 ) a n 1 a^{n}-a^{n-1} = (a-1)a^{n-1}

The above can be proved through simple distribution on the right side. What we have here is:

a n a n 1 a n 1 = ( a 1 ) a n 1 a n 1 = ( a 1 ) \frac{a^{n}-a^{n-1}}{a^{n-1}} = \frac{(a-1)a^{n-1}}{a^{n-1}} = (a-1)

In this case a is 9999 and n is 999. Regardless, the answer is a - 1, which is 9999 - 1, which is 9998.

Dave Williamson
Mar 4, 2018

Let A=9999^9998

(9999A - A) / A

9998A / A

9998

Jamie Redman
Feb 3, 2018

I split it into two fractions, 9999^999/9999^998 and -9999^998/9999^998. Using the index quotient rule, the first fraction can be evaluated to 9999^1, which is 9999. The second fraction’s denominator and numerator are equal (keep in mind it is negative) meaning it is 1 and so it is 9999 + -1 = 9998

Elliot Lee
Mar 24, 2017

imagine...

( 2 3 2 2 ) 2 2 \frac{(2^3 - 2^2)}{2^2} = a

2 3 2 2 = 2 2 a 2^3 - 2^2 = 2^2 * a

2 3 = ( 2 2 a ) + 2 2 2^3 = (2^2 * a) + 2^2

2 3 = ( a + 1 ) 2 2 2^3 = (a+1) * 2^2

2 3 / 2 2 = a + 1 2^3 / 2^2 = a+1

2 3 2 = a + 1 2^{3-2} = a+1

back to question:

999 9 999 998 = a + 1 9999^{999-998} = a+1

999 9 1 = a + 1 9999^1 = a+1

9999 1 = a 9999-1 = a

9998 9998

Sirajudheen Mp
Oct 19, 2015

{(9999^999)-(9999^998)}/9999^998}={(9999^998)(9999-1)}/9999^998=9999-1=9998

Delano Might
Oct 9, 2015

999 9 999 999 9 998 999 9 998 = 999 9 998 × ( 9999 1 ) 999 9 998 \frac {9999^{999} - 9999^{998}}{9999^{998}} = \frac {9999^{998}\times(9999 - 1)}{9999^{998}} = 9999 1 = 9998 = 9999 - 1 = 9998

Hitoshi Yamamoto
Oct 4, 2015

( (9999^999) - (9999^998) ) / (9999^998) = ( (9999^998)(9999-1) ) / (9999^998) = 9999-1 = 9998

So easy ( 9999^999 - 9999^998 ) / ( 9999^998) = ( 9999^998( 9999 - 1 ) ) / (9999^998) = 9999 -1 = 9998

Ratish Singh
Sep 15, 2015

9999^{999}-9999^{998}/9999^{998} Taking 9999^{998} common in the numerator, we get, 9999^{998}(9999-1)/9999^{998) Cancelling out the like terms, we get, 9999-1=9998

Lilik Irmawati
Sep 14, 2015

= (9999^998 (9999-1)) / 9999^998 = 9999-1 = 9998

Ismail Moumni
Sep 11, 2015

(9999^999 - 9999^998 )/9999^998

=[9999^998×(9999-1)]/9999^998

=9999-1 =9998

Keith Daggett
Sep 11, 2015

9999^9998(9999-1)/9998 = 9999-1 = 9998

Sadasiva Panicker
Sep 11, 2015

(9999^999 - 9999^998)/9999^998 = 9999^998(9999 - 1) /999^998 = 9999 - 1 = 9998

Mahmoud Rashidy
Sep 8, 2015

(9999^999-9999^998)/9999^998 = (9999^999/9999^998)-1 = 9999-1 = 9998

Hadia Qadir
Sep 7, 2015

x = 9999

-> (x^999 - x^998)/(x^998)

-> (x^999/x^998) - (x^998/x^998)

-> x - 1

= 9999 - 1

= 9998

Mahmoud Hamdy
Sep 7, 2015

{9999~998(9999-1)}/9999~998 = 9999-1 =9998

Tan Kenneth
Sep 4, 2015

well i just slove it in my head~ no sol hahahaha XD

Roberto Lassari
Sep 4, 2015

(9999^999 - 9999^998 )/(9999^998) = ( 9999^999)/ (9999^998) - (9999^998)/(9999^998) = 9999^(999-998) - 9999^(998-998) = 9999^1 - 9999^0 = 9999 - 1= 9998

Manish Sharma
Aug 26, 2015

The same as X raised to the power of n. You first take out the 9999 raise to power 8 of the two terms on the numerator And then you cancel the factors. Then you are left with 9999-1. The answer is 9998.

George Littles
Aug 24, 2015

9999^999 = 9999 * 9999^998 Therefore 9999^999 - 9999^998 = 9998 * 9999^9998. So if you divide by 9999^998 the you're left with only 9998

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