Ratios

Level 1

If the ratio of x + y x+y to x y x-y is 11 4 \frac{11}{4} , then the ratio of y y to x x can be written as a b \frac{a}{b} , where a a and b b are coprime positive integers. Find a + b a+b .


The answer is 22.

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25 solutions

Hahn Lheem
Dec 22, 2013

We can construct the ratio x + y x y = 11 4 \frac{x+y}{x-y}=\frac{11}{4} . Cross-multiplying gives us 4 x + 4 y = 11 x 11 y 4x+4y=11x-11y ; therefore, 7 x = 15 y 7x=15y . After further division, this gives us y x = 7 15 \frac{y}{x}=\frac{7}{15} . Our answer is 7 + 15 = 22 7+15=\boxed{22} .

this makes me feel dumb even though im the smartest in my grade

alex murphy - 7 years, 5 months ago

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Meet this whole website

Alex Li - 5 years, 3 months ago

nice solution ! I love you

La Bassa - 7 years, 5 months ago

We can write:

x + y : x y = 11 : 4 x + y : x - y = 11 : 4

x + y x y = 11 4 \frac{x + y}{x - y} = \frac{11}{4}

4 ( x + y ) = 11 ( x y ) 4(x + y) = 11(x - y)

4 x + 4 y = 11 x 11 y 4 x + 4 y = 11 x - 11 y

4 y + 11 y = 11 x 4 x 4 y + 11 y = 11 x - 4 x

15 y = 7 x 15 y = 7 x

y = 7 x 15 y = \frac{7 x}{15}

y x = 7 15 \frac{y}{x} = \frac{7}{15}

So, a = 7 a = 7 and b = 15 b = 15

Thus the answer is: a + b = 7 + 15 = 22 a + b = 7 + 15 = \boxed{22}

Saurabh Mallik - 7 years, 1 month ago
Prasun Biswas
Dec 22, 2013

We here use the method of componendo and dividendo according to which, if x y = a b x + y x y = a + b a b \frac{x}{y}=\frac{a}{b} \implies \frac{x+y}{x-y}=\frac{a+b}{a-b} . Given that, x + y x y = 11 4 \frac{x+y}{x-y}=\frac{11}{4}

It is said that, y x = a b \frac{y}{x}=\frac{a}{b}

x y = b a \implies \frac{x}{y}=\frac{b}{a}

x + y x y = b + a b a \implies \frac{x+y}{x-y}=\frac{b+a}{b-a}

11 4 = b + a b a \implies \frac{11}{4}=\frac{b+a}{b-a}

4 b + 4 a = 11 b 11 a 7 b = 15 a a b = 7 15 \implies 4b+4a=11b-11a \implies 7b=15a \implies \frac{a}{b}=\frac{7}{15}

So, now we have a b = 7 15 \frac{a}{b}=\frac{7}{15} where a and b are coprime, a=7 and b=15, so a + b = 7 + 15 = 22 a+b=7+15=\boxed{22}

Nice solution !

Devesh Rai - 7 years, 5 months ago

Perfect!

Heder Oliveira Dias - 7 years, 3 months ago

Same method!!! :D

Athiyaman Nallathambi - 5 years, 11 months ago

4 ( x + y ) = 11 ( x y ) 4(x+y)=11(x-y) 4 x + 4 y = 11 x 11 y 4x+4y=11x-11y 15 y = 7 x 15y=7x y x = 7 15 \frac{y}{x}=\frac{7}{15} a + b = 7 + 15 = 22 a+b=7+15=22

simple and good

Sathish Kumar - 7 years, 5 months ago

How it be possible that a=7 &b=15.A should be "7K"&b should be"15K".where 'k' is a constant.

Arshad Kamal - 7 years, 1 month ago

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Yeah , I too thought this way

Avb ... - 2 years, 1 month ago

a and b have to be coprime integers

Krish Shah - 1 year, 2 months ago
Kishore Kumar
Jan 5, 2014

given that : (x-y) : (x+y) = 11:4

there fore x:y = (11+4 ) : (11-4) ==>x:y = 15 : 7 as given x:y =a : b

we got a=15 and b=7 ==> (a+b)=15+7 = 22 Ans

Vivek kumar Gupta
Feb 20, 2017

We can construct the ratio X+Y/X-Y=11/4 . Cross-multiplying gives us ; therefore7X=15Y, . After further division, this gives usY/X=7/15=A/B . Our answer is7+5= .22

x + y = 11 x-y = 4 2x = 15 x = 15/2 Change x by 15/2, the result is 15/2 + y = 11 then y = 7/2 to gain y/x solution: 7/2(under this fraction put a long vinculum) over 15/2 then 7/2 times 2/15 is equals to 7/15. Therefore a + b = 7 + 15 = 22

(x+y)/(x-y)=11/4,

4(x+y)=11(x-y),

15y=7x,

y/x=7/15=a/b,

a+b=7+15= 22

Manish Kumar
Feb 4, 2014

method 1st- applying componendo and dividendo... method 2nd- dividing numetator and denominator of L.H.S. by x.

(x+y)/(x-y) = 11/4 then, (x+y+x-y)/(x+y-x+y) = (11+4)/(11-4) or, 2x/2y=15/7 or x/y=15/7 = b/a so a+b=15+7=22

Kamaljeet Singh
Jan 18, 2014

(x+y)/(x-y)=11/4 Let x/y=p (p+1)/(p-1)=11/4 here after calculaton p=15/7 a/b=15/7 a+b=15+7 =22

Indra Dutta
Jan 16, 2014

y/x=15/7;so a+b=15+7=22

Sandeep Sharma
Jan 16, 2014

(x+y)/(x-y)=11/4 =>4x+4y=11x-11y =>15y=7x =>y/x=7/15 there fore a+b=7+15=22

Escrevendo a razão de acordo com o que informa o problema:

x+y/x-y = 11/4 4x + 4y = 11x - 11y 15y = 7x

Então:

15/7 = a/b a + b = 15 + 7

Logo, a + b = 22.

Magdy Essafty
Jan 6, 2014

(x+y)/(x-y)=11/4 (1+k)/(1-k)=11/4 where k=y/x 4+4k=11-11k 15k=7 k=7/15 therefore a/b=15/7 a+b=22

Abhishek Sanghai
Jan 5, 2014

by componendo and dividendo

Vinit Kumar
Dec 30, 2013

x+y/x-y=11/4 4x+4y=11x-11y 7x=15y x/y=15/7 y/x=7/15 a+b=22

Sathish Kumar
Dec 27, 2013

by solving the equn x+y =11 x-y=4 we get x=15/2 y=7/2 while writing this in the ratio form we get a/b = 7/15 which corresponds a= 7 and b=15.....therefore a+b =22

Phanindra Sarma
Dec 23, 2013

If x/y=a/b, then x+y/x-y=a+b/a-b. This is called componendo and dividendo. Use that and you'll get the solution.

Kartikay Kumar
Dec 23, 2013

Cross multiply equation; find x x and y y ; find x y x\over y ; reduce to simplest terms; add; submit.

Ajay Maity
Dec 22, 2013

Given,

x + y x y = 11 4 \frac{x + y}{x - y} = \frac{11}{4}

Since we require y x \frac{y}{x} , we apply dividendo-componendo ,

( x + y ) ( x y ) ( x + y ) + ( x y ) = 11 4 11 + 4 \frac{(x + y) - (x - y)}{(x + y) + (x - y)} = \frac{11 - 4}{11 + 4}

2 y 2 x = 7 15 \frac{2y}{2x} = \frac{7}{15}

y x = 7 15 \frac{y}{x} = \frac{7}{15}

Hence, a + b = 7 + 15 = 22 a + b = 7 + 15 = 22

That's the answer!

Budi Utomo
Dec 22, 2013

(x + y ) : ( x - y) = 11/4 ---> 4x + 4y = 11x - 11y ---> 15y = 7x ---> y/x = 7/15. So,a + b = 7 + 15 = 22. Answer : 22

Hantu Pocong
Dec 22, 2013

(x + y)/(x - y) = 11/4

4x + 4y =11x -11y

7x = 15y

the addition of both coefficient of the unknowns = 22

Kartikay Kaul
Dec 22, 2013

22

Abhishek Pandey
Dec 22, 2013

x+Y/x-y +1 =11/4 +1: 2x/x-y = 15/4 -(1) x+y/x-y -1 = 11/4 - 1 ; 2y/x-y = 7/4 -(2) divide (1) by (2) we get x/y =15/7 so a+b= 15+ 7 = 22

Pollock Hasan
Dec 22, 2013

x+y/x-y=11/4, 2x/2y=15/7, x/y=15/7=b/a, a+b=15+7=22.

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