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# When a/b=1.2, (a-b)/(a+b)=?

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Math Revolution GMAT Instructor
Joined: 16 Aug 2015
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24 Apr 2017, 02:51
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97% (01:07) correct 3% (01:44) wrong based on 49 sessions

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When a/b=1.2, (a-b)/(a+b)=?

A. $$\frac{1}{15}$$
B. $$\frac{1}{11}$$
C. $$\frac{1}{9}$$
D. $$\frac{3}{8}$$
E. $$\frac{1}{3}$$

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"Only $99 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Manager Joined: 22 Jun 2016 Posts: 246 Re: When a/b=1.2, (a-b)/(a+b)=? [#permalink] ### Show Tags 24 Apr 2017, 03:41 When a/b=1.2, (a-b)/(a+b)=? Divide numerator and denominator by b. we get, (a/b-1)/(a/b+1) = (1.2-1)/(1.2+1) = 0.2/2.2 = 0.1/1.1 = 1/11 Hence, answer is B. _________________ P.S. Don't forget to give Kudos Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6371 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: When a/b=1.2, (a-b)/(a+b)=? [#permalink] ### Show Tags 26 Apr 2017, 01:17 ==> From a/b=1.2=6/5, if you substitute a=6 and b=5, you get (a-b)/(a+b)=(6-5)/(6+5)=1/11. Therefore, the answer is B. Answer: B _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
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26 Apr 2017, 01:22
1
MathRevolution wrote:
When a/b=1.2, (a-b)/(a+b)=?

A. $$\frac{1}{15}$$
B. $$\frac{1}{11}$$
C. $$\frac{1}{9}$$
D. $$\frac{3}{8}$$
E. $$\frac{1}{3}$$

Hey,

We can also apply componendo and dividendo to solve this question.

$$\frac{a}{b} = \frac{1.2}{1}$$

$$\frac{(a - b)}{(a + b)} = \frac{(1.2 - 1)}{(1.2 + 1)}$$

$$\frac{(a - b)}{(a + b)} = \frac{0.2}{2.2}$$

$$\frac{(a - b)}{(a + b)} = \frac{1}{11}$$

Hence correct answer is Option B.

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Saquib
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28 Apr 2017, 14:44
MathRevolution wrote:
When a/b=1.2, (a-b)/(a+b)=?

A. $$\frac{1}{15}$$
B. $$\frac{1}{11}$$
C. $$\frac{1}{9}$$
D. $$\frac{3}{8}$$
E. $$\frac{1}{3}$$

$$\frac{a}{b}$$ = 1.2

Multiply both sides by b

a = 1.2b

Let b = 10 (Choose a number that will yield an integer when multiplied by 1.2)

So a = (1.2)(10) = 12

(a-b) = 12 - 10 = 2
(a+b) = 12 + 10 = 22

$$\frac{(a-b)}{(a+b)}$$ ==> $$\frac{2}{22}$$ = $$\frac{1}{11}$$ Answer: B
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29 Apr 2017, 09:01
1
MathRevolution wrote:
When a/b=1.2, (a-b)/(a+b)=?

A. $$\frac{1}{15}$$
B. $$\frac{1}{11}$$
C. $$\frac{1}{9}$$
D. $$\frac{3}{8}$$
E. $$\frac{1}{3}$$

We are given:

a/b = 1.2

a = 1.2b

We need to determine the value of (a - b)/(a + b).

(a - b)/(a + b) = (1.2b - b)/(1.2b + b) = 0.2b/2.2b = 0.2/2.2 = 2/22 = 1/11

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Re: When a/b=1.2, (a-b)/(a+b)=? &nbs [#permalink] 29 Apr 2017, 09:01
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