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 the number of marbles that Pulak and Menaja had was 5:9 while the ratio of the number of marbles that Jairam and Menaja had was 7:18. What is the ratio of the number of marbles that Pulak and Jairam had?

 

A) 10:7 B) 2:3  
C) 5:7 D) 7:5
 
Answer & Explanation Answer: A) 10:7

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Q:

What is the fourth proportional to 6, 24 and 83?

A) 249 B) 332
C) 166 D) 498
 
Answer & Explanation Answer: B) 332

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Q:

In a college union, there are 48 students. The ratio of the number of boys to the number of girls is 5:3. The number of girls to be added in the union, so that the number of boys to girls in 6:5 is

A) 6 B) 7
C) 12 D) 17
 
Answer & Explanation Answer: B) 7

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Q:

In what ratio does the point T (3,0) divide the segment joining the points S (4,­2) and U (1,4)?

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

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Q:

What is the fourth proportional to 24, 120 and 22?

A) 110 B) 120
C) 100 D) 90
 
Answer & Explanation Answer: A) 110

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Q:

Three triangles are marked out of a bigger triangle at the three vertices such that each side of each of the smaller triangles is one-third as long as each corresponding side of the bigger triangle. The ratio of the area of the three small triangles taken together to that of the rest of the bigger triangle is ?

A) 1:2 B) 1:3
C) 3:1 D) 1:9
 
Answer & Explanation Answer: A) 1:2

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6 1220
Q:

The ratio of two numbers is 2 : 3. If the sum of both the numbers is 75, then what is the larger number among both the numbers?

A) 45 B) 30
C) 50 D) 48
 
Answer & Explanation Answer: A) 45

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Q:

If 2r = h + r2+h2, then the ratio of r:h is

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

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