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Question

If (2ab - b2) : (6a2 - ab) = 1 : 6, then what is the value of (a + b) : (a - b)?

This question was previously asked in
CDS II 2021 General Knowledge Previous Year Paper (14-Nov-2021)
The correct answer is

-5 or 5

Given:

(2ab - b2) : (6a2 - ab) = 1 : 6

Calculation:

We have,

(2ab - b2) : (6a2 - ab) = 1 : 6

⇒ 6 × (2ab - b2) = 1 × (6a2 - ab)

⇒ 12ab - 6b2 = 6a2 - ab

⇒ 6a2 - 13ab  + 6b= 0

⇒ 6a2 - 9ab - 4ab + 6b= 0

⇒ 3a (2a - 3b) - 2b (2a - 3b) = 0 

⇒ (2a - 3b) (3a - 2b) = 0 

⇒ (2a - 3b) = 0 or (3a - 2b) = 0 

⇒ 2a = 3b or 3a = 2b

Case:1   2a = 3b 

⇒ a : b = 3 :  2

⇒ (a + b) : (a - b) = (3 + 2) : (3 - 2) 

⇒ (a + b) : (a - b) = 5

Case:2    3a = 2b 

⇒ a : b = 2 : 3 

⇒ (a + b) : (a - b) = (2 + 3) : (2 - 3) 

⇒ (a + b) : (a - b) = -5

∴ The value of (a + b) : (a - b) is -5 or 5.

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Important Questions from Simple Ratios

  1. If x : y = 5 : 2, then the value of (8x + 9y) : (8x + 2y) is:

  2. If the value of \(\frac{{p - q}}{q} = \frac{4}{3}\)  .find p : q

  3. Two numbers are in the ratio of 9 : 7. If the larger number is 56 more than one-seventh of the smaller, then what is the sum of the two numbers?

  4. The ratio of two numbers A and B is 5: 8. If 5 is added to each of A and B, then the ratio becomes 2 : 3. The difference between A and B is:

  5. In population of a city the ratio of men and women is 12 : 11. If total population of that city is 4,60,000, then the population of women is:

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