Can You Multiply These Fractions?

Algebra Level 1

1 2 × 2 3 × 3 4 × 4 5 × × 9 10 = ? \Large \frac {\color{#D61F06}1} {\color{#3D99F6}2} \times \frac {\color{#D61F06}2} {\color{#3D99F6}3} \times \frac {\color{#D61F06}3} {\color{#3D99F6}4} \times \frac {\color{#D61F06}4} {\color{#3D99F6}5} \times \ldots \times \frac { \color{#D61F06}9}{ \color{#3D99F6}{10}} = \ ?


The answer is 0.1.

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22 solutions

Jackson Abascal
Nov 9, 2014

Since the multiplication of a series of fractions is the product of all the numerators over the product of all the denominators, we can find the answer with 9 ! 10 ! = 9 ! 9 ! ( 10 ) = 1 10 = 0.1 \frac { 9! }{ 10! } =\frac { 9! }{ 9!(10) } =\frac { 1 }{ 10 } =0.1 .

This seems more complicated than necessary. Just cancel before multiplying. Everything cancels except the 1 and the 10.

Michael Hardy - 6 years, 6 months ago

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It's actually simpler than writing out all of the fractions and cancelling. The 9! is the representation of that and shows that 9! cancels out 9!. Probably the simplest possible way to write it.

Jarod Morris - 6 years, 5 months ago

Could you articulate your equalities a bit more--still not following.

Still not clear on what 9!/10! means and where it came from, and then where the next fraction equality came from (9!/9!(10))

Robert Chesbro - 6 years, 4 months ago

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Robert, 9! means "nine factorial." It is a simple way to write sum of 9x8x7x6x5x4x3x2x1, which is what you do when you multiply all the numerators of this equation. The denominator is 10!. This is what you're doing when you multiply across all of the denominators. So the simplest way to way to write the equation is 9!/10! . Then, to go further, you factor out 9! from the fraction by dividing 9! from both the numerator and the denominator. So 9! divided by 9! = 1. And 10! divided by 9! = 10. That's how you get 1/10 or 0.1

Kyle Debro - 6 years, 4 months ago

It has yet another simple explanation.

Muthu Kaleeswaran - 6 years, 5 months ago

I typed correct answer(0. 1)But it showing that these values are not allowed

Akshay Jain - 4 years, 12 months ago

I'm mad. I kept trying to answer 1/10 & it wouldn't accept my answer, only to find out after checking the solution afterwards I needed to put the dumb answer as a decimal!

Mark Miedema - 4 years, 8 months ago

But why, when the problem statement used fractions, is not the answer 1/10 deemed acceptable?

John Gerig - 4 years, 3 months ago

@Jackson Abascal : You should cancel BEFORE multiplying.

Michael Hardy - 4 years, 2 months ago

Before you explained, I was totally confused! but now, ALL BETTER!

mash religion - 3 years, 6 months ago

Clarification to above reply: I understand the meaning of 9! / 10!

Not understanding how 9! / 9! (10) comes into being.

Robert Chesbro - 6 years, 4 months ago

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10! is simply 10 x 9 x8 x7 x6 x5 x4x3x2x1. which is the same as 9!(10)

Nathan Sikkema - 6 years, 3 months ago

The denominator of the previous fraction is cancelled by the numerator of the next fraction.This process gives 1 10 = 0.1 \frac{1}{10}=\boxed{0.1}

just as i did!

Aarush Kumbhakern - 5 years, 2 months ago

Ohhhhhhhh this makes much more sense now

Miciah Thacker - 4 years, 9 months ago

Oh, I cannot believe I did not see that before! It's so simple now!!!

mash religion - 3 years, 6 months ago

simple, removing the numeraror/denominator remaining will be 1/10

Hanta Julian
Nov 20, 2014
1 2 \frac {1}{2} * 2 3 \frac {2}{3} = 1 3 \frac {1}{3}
1 3 \frac {1}{3} * 3 4 \frac {3}{4} = 1 4 \frac {1}{4}
1 4 \frac {1}{4} * 4 5 \frac {4}{5} = 1 5 \frac {1}{5}
1 5 \frac {1}{5} * 5 6 \frac {5}{6} = 1 6 \frac {1}{6}
1 6 \frac {1}{6} * 6 7 \frac {6}{7} = 1 7 \frac {1}{7}
1 7 \frac {1}{7} * 7 8 \frac {7}{8} = 1 8 \frac {1}{8}
1 8 \frac {1}{8} * 8 9 \frac {8}{9} = 1 9 \frac {1}{9}
1 9 \frac {1}{9} * 9 10 \frac {9}{10} = 1 10 \frac {1}{10}
1 10 \frac {1}{10} = 0.1

Ok, now it makes sense even for me, :) thanx!

Raoul Wentzel - 5 years, 3 months ago
Chelsea Long
Jul 31, 2015

Just use cancellation. For example:

1/2 x 2/3 = 1/3, because the 2s cancel out.

1/3 x 3/4 = 1/4, because the 3s cancel out.

1/4 x 4/5 = 1/5, because the 4s cancel out.

Just continue this to the end, and you are left with 1/10.

1/10 = 0.1, so the answer is 0.1

Отлично! Самое простое объяснение, без всяких фракталов.

Иван Краевед - 4 years, 7 months ago
Achille 'Gilles'
Jan 2, 2016

1/10... the 2s cancels each others, the 3s, the 4s...

Kit Westman
Dec 30, 2017

1 2 \frac{1}{2} x 2 3 \frac{2}{3} x 3 4 \frac{3}{4} x 4 5 \frac{4}{5} x 5 6 \frac{5}{6} x 6 7 \frac{6}{7} x 7 8 \frac{7}{8} x 8 9 \frac{8}{9} x 9 10 \frac{9}{10} multiply it all together = 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 10 \frac{1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9}{2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x 10} rearrange the terms and split back into new fractions = 2 2 \frac{2}{2} x 3 3 \frac{3}{3} x 4 4 \frac{4}{4} x 5 5 \frac{5}{5} x 6 6 \frac{6}{6} x 7 7 \frac{7}{7} x 8 8 \frac{8}{8} x 9 9 \frac{9}{9} x 1 10 \frac{1}{10} turn fractions that are 1 into 1 = 1 x 1 x 1 x 1 x 1 x 1 x 1 x1 x 1 10 \frac{1}{10} 1 goes away in multiplication = 1 10 \frac{1}{10}

Kitty Saravanan
Jun 9, 2017

Cross out repeating numbers.

Syed Hamza Khalid
Feb 20, 2017

Cut out the denominator of the fraction by the next one - which means: - the answer is 0.1

Jay Kishan Cruz
Oct 14, 2016

All denominators are cancelled by the next of numerator. Only 1/10 will left so the answer is 0.1

Sarthak Sharma
Jul 28, 2016

Take logarithm both sides , assume right side as x , each successive log is canceled by previous member , in the end we are left with logx=log(1/10) , on comparing we get x=0.1

Ludovic Frérot
Feb 29, 2016

n ! ( n + 1 ) ! \frac{n!}{(n+1)!} , if n eq 9 we got 9 ! 10 ! \frac{9!}{10!} , eq 9 ! 9 ! ( 10 ) \frac{9!}{9!(10)} simplified by 1 10 \frac{1}{10} .

Anshuman Pal
Feb 27, 2016

9!/10! =9!/9!*10 =1/10 =0.1

Abdul Haseeb
Feb 24, 2016

The dr. Of the previous fraction is cancelled by the nr of next fraction. Then it gives 1/10=0.1

Garrison Wynn
Jan 3, 2016

the product of the numerators will be x, the product of the denominators will be 10x, therefpre the answer willbe x/10x=1/10

Caroline Lui
Nov 3, 2015

All of the numerators and denominators cancel except 1 and 10, ergo 1/10 or .1

Gokhul Prasad
Oct 29, 2015

9!/10! =1/10=0.1

Christopher Unrau
Oct 21, 2015

This fraction is equivalent to 9!/10! since 10!=9!*10, the 9! is cancelled out with only a ten left, so we have 1/10, which is 0.1.

Meenakshi Reji
Oct 18, 2015

All the numbers cancel off except 1 & 10 Leaving 1/10 = 0.1

Zaidah Maulidina
Jul 8, 2015

Remove 2, 3, 4, 5, 6, 7, 8, and 9. And you will find 1/10 and it means 0.1

Joel Shah
Jun 27, 2015

9! / 10, then we can cancel 9! making it 1/10 =0.1

Alex Menendez
Dec 14, 2014

The way I did it (which was a bit too much) was: Let n = 1 n = 1 , therefore, the product is written as: n n + 1 × n + 1 n + 2 × n + 2 n + 3 × n + 3 n + 4 × n + 4 n + 5 × n + 5 n + 6 × n + 6 n + 7 × n + 7 n + 8 × n + 8 n + 9 \frac{n}{n+1} \times \frac{n+1}{n+2} \times \frac{n+2}{n+3} \times \frac{n+3}{n+4} \times \frac{n+4}{n+5} \times \frac{n+5}{n+6} \times \frac{n+6}{n+7} \times \frac{n+7}{n+8} \times \frac{n+8}{n+9} But most of the the denominators cancel each other, leaving: n × 1 n + 9 = 1 10 = 0.1 n \times \frac{1}{n+9} = \frac{1}{10} = 0.1 \blacksquare

cancellation Method only,so we get 0.1 .. :)

Embran Fajardo - 5 years, 9 months ago

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