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 Ratios and Proportions Questions

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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, x∝y

(ii) We say that x is inversely proportional to y, if xy = k for some constant k and we write, x∝1y

Q:

Divide Rs.6500 among A,B and C so that after spending 90% , 75% and 60% of their respective saving were in the ratio of 3: 5: 6

Answer

A's spending 90%              \inline \therefore   saving = 10%


B's spending 75%              \therefore   saving = 25%


C's spending 60%              \inline \therefore   saving = 40%


Let us suppose A, B and C saves Rs. 3.5 and 6 respectively.


\inline \therefore 10% of A's saving = Rs.3


100% of A's saving = \inline \frac{3}{10}\times 100 = Rs. 30


25% of B's saving = Rs. 5


100% of B's saving = \inline \frac{5}{25}\times 100 = Rs. 20


40% of C's saving = Rs.6


100% of C's saving = \inline \frac{6}{40}\times 100 = Rs. 15


Divide Rs. 6500 in the ratio of 30 : 20 : 15 as


A's Share  =  \inline \frac{30}{65}\times 6500 = Rs. 3000


B's Share   = \inline \frac{20}{65}\times 6500 = Rs. 2000


C's Share  = \inline \frac{15}{65}\times 6500 = Rs. 1500

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Subject: Ratios and Proportions - Quantitative Aptitude - Arithmetic Ability
Job Role: Bank PO

64 8001
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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Subject: Ratios and Proportions - Quantitative Aptitude - Arithmetic Ability Exam Prep: AIEEE , Bank Exams , CAT
Job Role: Bank Clerk , Bank PO

60 12361
Q:

If the ratio of the ages of two friends A and B is in the ratio 3 : 5 and that of B and C is 3 : 5 and the sum of their ages is 147, then how old is B?

A) 27 Years B) 75 Years
C) 45 Years D) 49 Years
 
Answer & Explanation Answer: C) 45 Years

Explanation:

The ratio of the ages of A and B is 3 : 5.
The ratio of the ages of B and C is 3 : 5.

B's age is the common link to both these ratio. Therefore, if we make the numerical value of the ratio of B's age in both the ratios same, then we can compare the ages of all 3 in a single ratio.

The can be done by getting the value of B in both ratios to be the LCM of 3 and 5 i.e., 15.

The first ratio between A and B will therefore be 9 : 15 and
the second ratio between B and C will be 15 : 25.

Now combining the two ratios, we get A : B : C = 9 : 15 : 25.

Let their ages be 9x, 15x and 25x.
Then, the sum of their ages will be 9x + 15x + 25x = 49x

The question states that the sum of their ages is 147.
i.e., 49x = 147 or x = 3.

Therefore, B's age = 15x = 15*3 = 45

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57 22572
Q:

3 : 12 :: 5 : ?

A) 17 B) 30
C) 26 D) 32
 
Answer & Explanation Answer: B) 30

Explanation:

332 + 3 = 12552 + 5 = 30

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54 9583
Q:

A child has three different kinds of chocolates costing  Rs.2, Rs.5, Rs.10.  He spends total Rs. 120 on the chocolates. what is the minimum possible number of chocolates he can buy, if there must be  atleast one chocolate of each kind?

A) 22 B) 19
C) 17 D) 15
 
Answer & Explanation Answer: C) 17

Explanation:

Minimum number of chocolates are possible when he purchases maximum number of costliest chocolates.

Thus,          2 x 5 + 5 x 2 =Rs.20

Now Rs.100 must be spend on 10 chocolates as 100 = 10 x 10.

Thus minumum number of chocolates = 5 + 2 + 10 = 17

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48 17389
Q:

For any two numbers m , n ; (m+n) : (m-n) : mn = 7: 1: 60 . Find the value of 1/m : 1/n

A) 4:3 B) 8:7
C) 3:4 D) 7:8
 
Answer & Explanation Answer: C) 3:4

Explanation:

m+nm-n=7xx ⇒mn=4x3x  

 

Again   mn=12x2 

 

and         mn =60x  

 

so, 60x=12x2 ⇒x=5    

 

=>  m= 20  and    n= 15

 

Hence,    1m:1n=120:115=3:4

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47 15313
Q:

One year ago the ratio between Maneela’s and Shanthi’s salary was 3 : 4. The ratios of their individual salaries between last year’s and this year’s salaries are 4 : 5 and 2 : 3 respectively. At present the total of their salary is Rs. 4160. The salary of Maneela, now is?

A) Rs. 1600 B) Rs. 1700
C) Rs. 1800 D) Rs. 1900
 
Answer & Explanation Answer: A) Rs. 1600

Explanation:

Let the salaries of Maneela and Shanthi one year before be M1, S1 & now be M2, S2 respectively.

Then, from the given data,

M1/S1 = 3/4  .....(1)

M1/M2 = 4/5 .....(2)

S1/S2 = 2/3  .....(3)

and M2 + S2 = 4160  .....(4)

 

Solving all these eqtns, we get M2 = Rs. 1600.

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47 11448
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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