Ratios and Proportions Questions

FACTS  AND  FORMULAE  FOR  RATIO  AND  PROPORTION  QUESTIONS

 

 

1. RATIO: The ratio of two quantities a and b in the same units, is the fraction a/b and we write it as a:b.

In the ratio a:b, we call a as the first term or antecedent and b, the second term or consequent.

Ex. The ratio 5: 9 represents 5/9 with antecedent = 5, consequent = 9.

Rule: The multiplication or division of each term of a ratio by the same non-zero number does not affect the ratio. Ex. 4: 5 = 8: 10 = 12: 15 etc. Also, 4: 6 = 2: 3.

 

2. PROPORTION : The equality of two ratios is called proportion

If a: b = c: d, we write, a: b :: c : d and we say that a, b, c, d are in proportion . Here a and d are called extremes, while b and c are called mean terms.

Product of means = Product of extremes.

Thus, a: b :: c : d <=> (b x c) = (a x d).

 

 3(i) Fourth Proportional : If a : b = c: d, then d is called the fourth proportional to a, b, c.

     (ii) Third Proportional : If a: b = b: c, then c is called the third proportional to a and b.

     (iii) Mean Proportional : Mean proportional between a and b is ab

 

 4. (i) COMPARISON OF RATIOS : We say that (a: b) > (c: d)  (a/b)>(c /d).

     (ii) COMPOUNDED RATIO : The compounded ratio of the ratios (a: b), (c: d), (e : f)  is    (ace: bdf)

 

5. (i) Duplicate ratio of (a : b) is a2:b2.

    (ii) Sub-duplicate ratio of (a : b) is (√a : √b).

    (iii)Triplicate ratio of (a : b) is a3:b3.

    (iv) Sub-triplicate ratio of (a : b) is a13: b13.

    (V) If ab=cd, thena+ba-b=c+dc-d (Componendo and dividendo)

 

 6. VARIATION:

(i) We say that x is directly proportional to y, if x = ky for some constant k and we write, xy

(ii) We say that x is inversely proportional to y, if xy = k for some constant k and we write, x1y

Q:

Choose the CORRECT option about the two tangents drawn to the circle from the external point?

(1) The tangents subtend equal angles at the centre of the circle.

(2) The tangents drawn from the external point to a circle are equal in length.

(3) The tangents are equally inclined to the segment which joins the centre to that point.

A) 1 and 2 only B) 2 and 3 only
C) 1, 2 and 3 D) 1 and 3 only
 
Answer & Explanation Answer: C) 1, 2 and 3

Explanation:
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Q:

If u : v : w = 3 : 6 : 8, then what will be the ratio of (u/v) : (v/w) : (w/u)?

 

A) 8 : 6 : 3   B) 8 : 4 : 3  
C) 5 : 9 : 12   D) 6 : 9 : 32
 
Answer & Explanation Answer: D) 6 : 9 : 32

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Q:

Based on the analogy given, find the missing number from the given options.

 

11 : 13 :: 17 : ___

 

A) 29 B) 21
C) 19 D) 23
 
Answer & Explanation Answer: D) 23

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2 12146
Q:

If x : y = 1 : 3, then what will be the ratio of (3y2 + 3x2) : (2y2 - 8x2)?

 

A) 4 : 1   B) 2 : 1  
C) 3 : 1   D) 5 : 1
 
Answer & Explanation Answer: C) 3 : 1  

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Q:

Two numbers are in the ratio 3 : 7. If 6 be added to each of them, then they are in the ratio 5 : 9. Find the numbers ?

A) 11 & 17 B) 7 & 17
C) 9 & 21 D) 13 & 23
 
Answer & Explanation Answer: C) 9 & 21

Explanation:

Let the two numbers be x and y

Given x : y = 3 : 7 .....(1)

Now, x+6 : y+6 = 5 : 9 .....(2)

From (1), x = 3y/7

From (2), 5y - 9x = 24

=> 5y - 9(3y/7) = 24

=> y = 21

=> From(1), x = 9

Hence, the two numbers be 9 and 21

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36 11561
Q:

Two solutions have milk & water in the ratio 7:5 and 6:11. Find the proportion in which these two solutions should Be mixed so that the resulting solution has 1 part milk and 2 parts water ?

A) 7 : 12 B) 8 : 13
C) 9 : 4 D) 2 : 5
 
Answer & Explanation Answer: B) 8 : 13

Explanation:

To get the solution that contains 1 part of milk and two parts of water,
they must be mixed in the ratio as
7x+6x/5y+11y = 1/2
26x = 16y
x/y = 16/26
x/y = 8/13

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19 11547
Q:

Seats for Mathematics, Physics and Biology in a school are in the ratio 5 : 7 : 8. There is a proposal to increase these seats by 40%, 50% and 75% respectively. What will be the ratio of increased seats ?

A) 1 : 2 : 3 B) 2 : 3 : 4
C) 3: 4 : 5 D) 4 : 5 : 6
 
Answer & Explanation Answer: B) 2 : 3 : 4

Explanation:

Seats for Mathematics, Physics and Biology in a school are in the ratio 5 : 7 : 8.

Seats for Mathematics, Physics and Biology in a school are 5x, 7x and 8x.

There is a proposal to increase these seats by 40%, 50% and 75% respectively.

Then Seats for Mathematics, Physics and Biology in a school will be

1.4 X 5x, 1.5 X 7x and 1.75 X 8x and

ratio will be 7 : 10.5 : 14  => 2:3:4.

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Q:

16 : 56 :: 32 : ?

A) 196 B) 148
C) 132 D) 112
 
Answer & Explanation Answer: D) 112

Explanation:

16 : 56 :: 32 : ?

Let the required number be 'n'

The given numbers follow a logic that,

16/56 = 2/7

=> 32/n = 2/7

=> 32 x 7/2 = n

=> n = 112.

 

Hence, 16 : 56 :: 32 : 112.

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