Inverse addition is repeated addition?

Algebra Level 2

True or false

3 13 3 16 = 3 13 × 3 16 . \frac{ 3 } { 13} - \frac{3}{16} = \frac{3}{13} \times \frac{3}{16}.

False True

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

7 solutions

Pi Han Goh
Mar 20, 2015

Consider the general case: 1 n 1 n + m = ( n + m ) ( n ) n ( n + m ) = m n ( n + m ) \frac {1}{n} - \frac {1}{n+m} = \frac { (n+m) - (n)}{n(n+m)} = \frac {m}{n(n+m)}

Then

m n m n + m = m 2 n ( n + m ) = m n × m n + m \frac {m}{n} - \frac {m}{n+m}= \frac {m^2}{n(n+m)} = \frac {m}{n} \times \frac {m}{n+m}

, in this case m = 3 , n = 13 m=3,n=13 , so it's true! Hi Kevin!

That's how I came up with this question, from partial fractions.
I wanted to play with 2 + 2 = 2 × 2 2 + 2 = 2 \times 2 , and come up with a similar equation which didn't look believable.

Chung Kevin - 6 years, 2 months ago
Layba Durrani
Mar 22, 2015

we can simply solve both sides of equation the answer is 9/208=9/208

Yup. Is there any other reason why they are equal without expanding all the terms?

Chung Kevin - 6 years, 2 months ago
David Holcer
Mar 20, 2015

Why is this lvl. 3. lol, nice problem, but just compute each side. (3/13=48/208)-(3/16=39/208)=9/208 and then (3^2/13*16)=9/208 and 9/208=9/208 therefore the statement is true.

I think that most people are too lazy to compute both sides, and think that it is very unlikely to be true.

Chung Kevin - 6 years, 2 months ago

wtf, just take 3 common outta the LHS and cancel it with one 3 from the RHS, which leaves you with (1/13)-(1/16)=3/16x1/13 =>(16-13)/(16x13)=3/(16x13) =>3/(16x13)=3/(16x13)

simple as pie...clear as day!!!

Somesh Singh - 6 years, 2 months ago

I started to suspect the equation when I noticed the difference of the two denominators equals the numerator. After that it wasn't a hard choice.

Tom Guo - 6 years, 2 months ago
. .
Feb 10, 2021

3 13 3 16 = 48 208 39 208 = 9 208 \frac{3}{13} - \frac{3}{16} = \frac{48}{208} - \frac{39}{208} = \frac{9}{208} , and 3 13 × 3 16 = 9 208 \frac{3}{13} \times \frac{3}{16} = \frac{9}{208} . So they are same number.

Oli Hohman
Dec 17, 2015

Find LCD on both sides of the equation. What I usually do to find this is just multiply the two denominators together, and then check to see if half the product of the two numbers is divisible by both factors to ensure that the result is irreducible.

13*16 = 208, which isn't divisible by BOTH 13 and 16, so it is the LCD.

(3 * 16)/(13 * 16) - (3 * 13)/(13 * 16) = 9/(13 * 16)

Since the denominators are all equal, set the numerators equal on each side once you have the LHS under one denominator.

48/208 - 39/208 = 9/208 9/208 = 9/208, so it's true.

Gamal Sultan
Mar 22, 2015

(3/13) - (3/16) = [3(16) - 3(13)]/(13)(16) = (3)(3)/(13)(16) = (3/13) X (3/16)

So , the equation is true

Abhishek Pokala
Mar 22, 2015

3/13 - 3/16 = 3(16)- 3(13)/ 13 16 = 3( 16-13)/13 16 = 9/13*16.

3X3/13 16 = 9/13 16

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...