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:

The ratio of Pens and Pencils in a shop is 3 : 2 respectively. The average number of Pens and Pencils is 180. What is the number of Pencils in the shop? 

A) 444 B) 344
C) 244 D) 144
 
Answer & Explanation Answer: D) 144

Explanation:

Given ratio of pens and pencils = 3 :2

Number of Pens = 3x

Number of Pencils = 2x

Average number of pencils & Pens = 3x + 2x2 = 180

5x = 360

=> x = 72


Hence, the number of pencils = 2x = 72 x 2 = 144.

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36 16150
Q:

The third proportional tox2-y2 and x-y is :

A) (x + y ) B) (x - y)
C) (x + y) / ( x - y) D) (x -y) / ( x + y)
 
Answer & Explanation Answer: D) (x -y) / ( x + y)

Explanation:

Let the third proportional to x2-y2 and x-y be z. Then, 

 

x2-y2:x-y::x-y:z  

 

=>x2-y2*z=x-y2  

 

=> z=x-y2x2-y2=x-yx+y

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65 16130
Q:

In Maa Yatri Temple every devotee offers fruits to the orphans. Thus every orphan receives bananas, oranges and grapes in the ratio of 3:2:7 in terms of dozens. But the weight of a grape is 24 gm and  weight of a banana and an orange are in the ratio of 4:5, while the weight of an orangeis 150gm. Find the ratio of all the three fruits in terms of weight, that an orphan gets

A) 90:75:42 B) 180:150:82
C) 75:42:90 D) None of these
 
Answer & Explanation Answer: D) None of these

Explanation:

Ratio of fruits (by dozen) = 3:2:7

Ratio of fruits (by weight) =  120 :150: 24

Therefore, Ratio of fruits (combined) by weight = 3 x 120 : 2 x 150 : 7 x 24 = 30 : 25 : 14 

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16 15860
Q:

There is certain numbers of toys in the box. They are divided into such a way that the person who gets 1/4 of the whole gets thrice of what the others get on an average. Find the number of people amongst whom the toys are distributed?

A) 8 B) 10
C) 12 D) 9
 
Answer & Explanation Answer: B) 10

Explanation:

If the person who gets 1/4 of the whole gets thrice of what the others get on an average, each one will get =1/3×1/4=112 of the whole.
Therefore, if there are k persons other than the person who gets one-fourth, then 1/4 + k/12 = 1
⇒ k=9

Hence, total number of people = 10.

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34 15618
Q:

The ratio of boys and girls in a school is 9:5.If the total number of students in the school is 1050.Then number of boys is

Answer

Let the ratio be 'R'


Total number of students = 1050


Then,


9R + 5R = 1050


14R = 1050


=> R = 75


 


Hence, the number of boys = 9R = 9 x 75 = 675

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69 14929
Q:

The sum of three numbers is 98. If the ratio of the first to second is 2 : 3 and that of the second to the third is 5 : 8, then the second number is:

A) 10 B) 20
C) 30 D) 40
 
Answer & Explanation Answer: C) 30

Explanation:

Let the three parts be A, B, C. Then,

A : B = 2 : 3 and B : C = 5 : 8 =5*35:8*35=  3:245  

A : B : C = 2 : 3 : =>  = 10 : 15 : 24

 

 B =245 = 30

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Q:

If A : B = 2 : 3 and B : C = 4 : 5, then what is (A + C) : B?

 

A) 8 : 5 B) 7 : 3
C) 23 : 12 D) 25 : 14
 
Answer & Explanation Answer: C) 23 : 12

Explanation:
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Q:

64 boys and 40 girls form a group for social work. During their membership drive, the same number of boys and girls joined the group. How many members does the group have now, if the ratio of boys to girls is 4:3 ?

A) 168 B) 201
C) 147 D) 154
 
Answer & Explanation Answer: A) 168

Explanation:

Let us say x boys and x girls joined the group.

(64 + x)/(40 + x) = 4/3

192 + 3x = 160 + 4x => x = 32

Number of members in the group = 64 + x + 40 + x

= 104 + 2x = 168.

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