Solve this quickly!

Which is larger?

10 7 or 7 10 \LARGE \color{#D61F06}{10}^{\color{#3D99F6}{7}} \quad \text{or} \quad \color{#3D99F6}{7}^{\color{#D61F06}{10}}

1 0 7 10^7 7 10 7^{10} Equal

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30 solutions

Otto Bretscher
Aug 17, 2015

7 10 = 4 9 5 > 4 0 5 = 4 5 × 1 0 5 > 1 0 7 7^{10}=49^{5}>40^5=4^5\times10^5>10^7 since 4 5 = 1024 4^5=1024

a = 1 0 7 , b = 7 10 , a 1 0 7 = 1 , b 1 0 7 = 7 10 1 0 7 = 7 3 7 7 ( 10 ) 7 = 7 3 ( 7 10 ) 7 a=10^{7},b=7^{10} , \frac{a}{10^{7}}=1, \frac{b}{10^{7}}= \frac{7^{10}}{10^{7}}= \frac{7^{3}*7^{7}}{(10)^{7}}= 7^{3} * (\frac{7}{ 10})^{7} >1 then b>a

Muh Ali - 5 years, 7 months ago

Otto brestcher......how did you observe this amazing fact

Bishwayan Ghosh - 2 years, 5 months ago

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More than 15k observed this fact from last 12000 years of dressed tail less ape civilisation

Theerdala Vignesh - 6 months, 1 week ago

Wow that's a brilliant answer

Sareeta Devi - 2 years, 3 months ago
Vubon Roy
Aug 17, 2015

take log , log 10^7 = 7 log 10 = 7 x 1 = 7 and log7^10 = 10 log 7 = 10 x 0.84 = 8.45

so B > A

kindly dear Roy , let me know how you reached the log values?

Jafir Khan Niazi - 5 years, 9 months ago

please tell me why you multiply 0.84 with 10??

Ariful Ashiq - 5 years, 9 months ago

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value of log7 is 0.8

Tarun Bunny - 5 years, 9 months ago

I did a similar method but didnt find the values of the log

Diyah Muhammed - 4 years, 6 months ago
汶良 林
Aug 11, 2015

7 10 > 4 9 5 > 3 2 5 = 2 25 = 2 7 × 2 18 = 2 7 × 3 2 3.6 > 2 7 × 2 5 3.5 = 2 7 × 5 7 = 1 0 7 7^{10} > 49^{5} > 32^{5} = 2^{25} = 2^{7}×2^{18} = 2^{7}×32^{3.6} > 2^{7}×25^{3.5} = 2^{7}×5^{7} = 10^{7}

2 7 × 2 18 2 7 × 3 2 3.6 2^7 \times 2^{18} \color{#D61F06}\geq 2^7 \times 32^{3.6}

Cleres Cupertino - 5 years, 10 months ago

Excellent!

Exponent Bot - 3 years, 2 months ago

7^10=49^5*

Adit Goud - 5 years, 10 months ago

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Or 7 10 4 9 5 7^{10}\color{#D61F06}\geq 49^5

Cleres Cupertino - 5 years, 10 months ago

7 10 = 282475249 , 1 0 7 = 10000000 7^{10} = 282475249, 10^{7} = 10000000

7 10 > 1 0 7 7^{10} > 10^{7}

Actually, this is easier!

汶良 林 - 5 years, 10 months ago

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Sure, if you have a calculator and trust it and yourself not to make mistakes.

Whitney Clark - 5 years, 10 months ago

Consider the function, y=x^{1/x}. Evaluate dy/dx and it turns out to be x^{(1/x)-2} (1-ln x), which when equated to zero gives x=e. Note that dy/dx >0 for x <e, dy/dx=0 for x=e and dy/dx <0 for x>e. Therefore the function y=x^{1/x} is a decreasing function when x>e. Hence, for x1>x2>e, x2^{1/x2} > x1^{1/x1}.

Since 10>7>e, 7^(1/7) > 10^(1/10). Raisiing the power to 70 on both sides, 7^10 > 10^7

Jiten Kashyap
Sep 13, 2015

7x7x7x7x7x7x7x7x7x7=282475249>10x10x10x10x10x10x10=1000000

Ahmed Kishk
Oct 6, 2015

Simply 10^7 is (0.01)^10 which is less than 7^10 :) :)

This is funniest logic here. XD Go back to 6th grade

Saurabh Sharma - 5 years, 8 months ago

10^7 is not the same as (0.01)^10...

Jana Carpinato - 4 years, 4 months ago
Jagreuben Singh
Aug 17, 2015

282475249>10000000 probably B is correct

Munem Shahriar
Jul 4, 2017

For 1 0 7 10^7 there will be seven zeroes after one

1 0 7 = 10 × 10 × 10 × 10 × 10 × 10 × 10 = 10000000 10^7 = 10 \times 10 \times 10 \times 10 \times 10 \times 10 \times 10 = 10000000

Now,

7 10 = 4 9 5 7^{10} = 49^5 or 282475249 282475249

Therefore 7 10 7^{10} is larger.

Mohammad Khaza
May 17, 2017

if i take log ,then log 10^7=7 log 10=7 and log 7^10=10 log 7=8.4509804(calculator). so,7^10 is bigger

i did it in the same way

Halima Tahmina - 4 years ago

thanks.your comment inspired me

Mohammad Khaza - 4 years ago
Daniel Leite
Sep 13, 2015

If you know that 7 3 = 343 7^3 = 343 , then you can estimate that 7 6 = 34 3 2 7^6 = 343^2 is a little greater than 100000 = 1 0 5 100000 = 10^5 .

With that in mind, base 10 logarithms tell us that log ( 7 6 ) log ( 1 0 5 ) 6 log 7 5 log 7 5 6 \log(7^6)\ge\log(10^5)\;\Rightarrow\;6\log7\ge5\;\Rightarrow\;\log7\ge\frac56 .

Thus, log ( 7 10 ) = 10 log 7 10 5 6 = 25 3 \log(7^{10}) = 10\log7 \ge 10\cdot\frac56 = \frac{25}3 .

Since log ( 1 0 7 ) = 7 < 25 3 \log(10^7) = 7 < \frac{25}3 , then log ( 1 0 7 ) < log ( 7 10 ) \log(10^7) < \log(7^{10}) , which means 7 10 > 1 0 7 7^{10} > 10^7 .

the best answer i saw ..u don't have to use a calculator but not a quickly one :D

Ibrahim Said - 5 years, 8 months ago
Chiew KSeng
Aug 18, 2015

I'm wondering why there isn't anybody who used log to solve this: 10log7 =10x0.9..... >0.9 > 7log10=7

Hadia Qadir
Aug 17, 2015

Using logarithms, it is easy to see that 7^10 is the larger number. But, actually, common sense with numbers would allow you to intuit correctly that 7^10 is the larger number.

= 7 10 . . . 1 0 7 7^{10} ... 10^{7} , = 7 3 7^{3} ... 10 10 , = 343 > 10 = 343 > 10 . So, 7 10 > 1 0 7 7^{10} > 10^{7}

Varun Mehra
Sep 26, 2016

Since power is bigger number of significant figures is more thus 7^10 is bigger than 10^7.

J Chaturvedi
Jan 16, 2016

7^10>6^10=6^7×6^3 6^3=2^3×3^3>2^3×2^4=>2^7 Therefore, 7^10>6^10>6^7×2^7=12^7>10^7 Hence proved

Karen Black
Nov 6, 2015

I cheated and used the fact that I have the first ten powers of 2 memorized:

4<7<8, so (4^10)<(7^10)<(8^10)

4^10=(2^10)^2 or roughly 10^6

8^10=(2^10)^3 or roughly 10^9

7 is closer to 8, so 7^10 is going to be closer to 10^9 which is larger than 10^7

Delonraj Delonraj
Oct 20, 2015

10 exponent 7 = 100M 7 exponent 10 =70B therefore 7 exponent 10 is larger than 10 exponent 7.

Priyaveda Janitra
Sep 26, 2015

simply count the digit roughly... just multiply and count the digit and you will find which one is bigger

Thiru Murugan
Sep 21, 2015

But how to generalize this concept for any two numbers a & b, where as a > b ? Any friend can clear ?

x 1 , x 2 x_1, x_2 , If x 1 , x 2 > e x_1, x_2>e

\Rightarrow If x 1 > x 2 x_1>x_2 then x 2 x 1 > x 1 x 2 x_2^{x_1}>x_1^{x_2} and vice versa...

Kishore S. Shenoy - 5 years, 8 months ago
Niem Ng
Sep 15, 2015

f(x) = ln(x)/x (x>=1); lim as x --> +infinity of f(x) = 0 so ln(x1)/x1 > ln(x2)/x2 with x1 < x2 (ln7)/7 > (ln10)/10 => 10ln7 > 7ln10 => ln(7^10) > ln(10^7) => 7^10 > 10^7

Genta Adithya
Sep 14, 2015

Subtitution with ~30% so it goes like this ::: 7^3 = 343 /// 10^2 = 100 so 10^2.1 should be just around 100. Which larger ? You dont even have using calculator.. Prove yourself :)

Ahsan Azhar
Sep 14, 2015

Check this one...... Log 10^7 < log 7^10...... 7log 10 < 10 log 7 ...... 7x1 < 10x0.84

Sanath Kumar B P
Sep 14, 2015

10^7 ? 7^10

1 ? .7^7*7^3

1? (.7)*(3.43)^3

70% of 3 itself is greater than 1

So 1< (.7)*(3.43)^3

Hence 7^10 is bigger.

Animesh Jha
Sep 14, 2015

We know that 7^8 > 10^7, and therefore 7^10 >> 10^7. Thats it

Bahy Eldein
Sep 13, 2015

every time you multiply with 7 you add number that is mean the final number will consist of 10 numbers

Jamil Nizamani
Sep 13, 2015

2^3=8,3^2=9 and 3^4=81,4^3=64 when the power is greater than base product is greater.So 7^10 is greater than 10^7

Alexandre Campos
Sep 13, 2015

Let's put "?" for our relation.

10⁷ ? 7¹⁰ log(10⁷) ? log(7¹⁰) [apply log, which is increasing, so the "?" sign stays the same] 7.log(10) ? 10.log(7) [log property] 7 ? 10.log(7) [log(10=1)]

Now, log(7)>1, so, 10 log(7)>10, therefore 7 < 10.log(7) which means that "?" = "<" and then

10⁷ < 7¹⁰

Bala Sundarm
Aug 17, 2015

(7/10)^7=0.7^7, this value may be less than one but after a point you will have some number. remaining 7^3 =21. if you multiply both ,the answer must be larger than one.so answer wold be B

Aaron Retzer
Aug 17, 2015

10^7=(7x1.43)^7 so divide both by 7^7 so 1.43^10 versus7^3 is no brainer 7^3 is much larger

Roy Belovoskey
Aug 7, 2015

Think of these spatially!

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