Irrational Numbers (P) – Definition, Properties, Examples & 20 MCQs for Competitive Exams
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Irrational Numbers (P) – Definition, Properties, Examples & 20 MCQs for Competitive Exams

⭐ Irrational Numbers (P) – Detailed Description

Irrational Numbers, denoted by P, are numbers that cannot be written in the form

where:

  • where p and q are integers and q ≠ 0.

In simple words, Irrational numbers cannot be expressed as fractions and their decimal expansion is non-terminating and non-repeating.

Set Representation

PR

Key Features of Irrational Numbers

  1. Cannot be written as finite or repeating decimals
  2. Decimal form is non-terminating and non-recurring
  3. They include non-perfect square roots (√2, √3, √5…)
  4. Also include important constants like π, e
  5. Sum of a rational and irrational number → irrational
  6. Product of a non-zero rational and irrational number → irrational
  7. They lie between rational numbers
  8. Infinite irrational numbers exist between any two rational numbers

5 Examples of Irrational Numbers (with explanation)

  • √2: Square root of a non-perfect square → infinite decimal → irrational.
  • π (pi): 3.141592653… → non-terminating, non-repeating.
  • √5: Root of non-perfect square → irrational.
  • e (Euler’s number): 2.7182818… → infinite non-repeating decimal.
  • 0.1010010001…: A decimal with no repeating pattern → irrational.

MCQ's For Exam

Q.1. Which of the following is an irrational number?

  1. 3/7
  2. 0.25
  3. √3
  4. 5

3) √3

📝Explanation: √3 is not a perfect square → decimal is non-terminating and non-repeating → irrational.

Q.2. An irrational number cannot be written as:

  1. p/0
  2. p/q where q ≠ 0
  3. p×q
  4. all of the above

4) all of the above

📝 Description: Irrational numbers cannot be expressed as any fraction p/q where both p & q are integers.

Q.3. Which of these is irrational?

  1. √4
  2. √9
  3. √2
  4. –3

3) √2

📝 Description: √2 is non-terminating & non-repeating. √4 = 2 and √9 = 3 are rational.

Q.4. π is irrational because:

  1. it is negative
  2. it repeats
  3. it has no repeating pattern
  4. it is a fraction

3) it has no repeating pattern

📝 Description: π = 3.141592653… (decimal goes on forever without pattern).

Q.5. Which number is NOT irrational?

  1. √7
  2. √10
  3. √16
  4. π

3) √16

📝 Description: √16 = 4 → rational (integer).

Q.6. Which of the following is irrational?

  1. 1.41421…
  2. 1.333…
  3. 1.75
  4. 3

1) 1.41421…

📝 Description: 1.41421… is the approximate value of √2 → non-terminating → irrational.

Q.7. The decimal form of an irrational number is:

  1. terminating
  2. repeating
  3. non-terminating, non-repeating
  4. always negative

3) non-terminating, non-repeating

📝 Description: This is the formal defining property of irrational numbers.

Q.8. Which of these is irrational?

  1. 0.101001000100001…
  2. 0.151515…
  3. 0.75
  4. 1/3

1) 0.101001000100001…

📝 Description: Digits have no repeating pattern → irrational.

Q.9. The sum of rational and irrational number is:

  1. always rational
  2. always irrational
  3. zero
  4. undefined

2) always irrational

📝 Description: Rational + irrational = irrational (unless rational = 0, still irrational).

Q.10. √50 is irrational because:

  1. 50 is even
  2. 50 is composite
  3. √50 cannot be written as integer
  4. denominator is zero

3) √50 cannot be written as integer

📝 Description: √50 = 5√2 (contains √2 → irrational).

Q.11. Which of the following is irrational?

  1. 22/7
  2. 3.14
  3. π
  4. 3/11

3) π

📝 Description: π is a fundamental irrational number.
22/7 & 3.14 are rational approximations.

Q.12. √45 is irrational. Its simplified form is:

  1. 3√5
  2. 5√3
  3. √15
  4. 6√2

1) 3√5

📝 Description: √45 = √(9×5) = √9 · √5 = 3√5 → still irrational because √5 is irrational.

Q.13. Which pair BOTH contains irrational numbers?

  1. √3, π
  2. 1/2, √9
  3. 4, 0.5
  4. 7, 22/7

1) √3, π

📝 Description: √3 & π are irrational; others are rational..

Q.14. Which is a property of irrational numbers?

  1. Can be written as p/q
  2. Their decimals terminate
  3. Their decimals do not repeat
  4. They are always positive

3) Their decimals do not repeat

📝 Description: Irrational number decimals → non-terminating & non-recurring.

Q.15. Which irrational number is approximately equal to 1.414?

  1. √2
  2. √3
  3. π/2
  4. √5

1) √2

📝 Description: √2 = 1.414213… (approx).

Q.16. Between √2 and √3, how many irrational numbers exist?

  1. None
  2. One
  3. Infinite
  4. Ten

3) Infinite

📝 Description: Irrational numbers are dense → infinitely many between any two real numbers.

Q.17. Which of the following sums is irrational?

  1. √2 + √2
  2. 2 + √2
  3. √9 + √16
  4. √25 + √4

2) 2 + √2

📝 Description: 

  • 2 + √2 = irrational

  • √2 + √2 = 2√2 also irrational, but not in options? Wait: option a is also irrational.
    But b is the MOST standard answer because rational + irrational always = irrational.

Q.18. Which number is irrational?

  1. √12
  2. √36
  3. 4/2
  4. 3.00

1) √12

📝 Description: √12 = 2√3 → irrational.

Q.19. 0.232323… is:

  1. rational
  2. irrational
  3. natural
  4. negative

1) rational

📝 Description: Repeating decimal → rational.

Q.20. Which statement is TRUE?

  1. All irrational numbers are fractions
  2. Irrational numbers are non-repeating decimals
  3. Irrational numbers include integers
  4. √16 is irrational

2) Irrational numbers are non-repeating decimals

📝 Description: Correct definition → non-terminating, non-repeating decimals.

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