CBSE Class 9 Mathematics Question 1 of 9

Number Systems — Question 1

Back to all questions
1
Question

Question 1

Write the following in decimal form and say what kind of decimal expansion each has :

(i) 36100\dfrac{36}{100}

(ii) 111\dfrac{1}{11}

(iii) 4184\dfrac{1}{8}

(iv) 313\dfrac{3}{13}

(v) 211\dfrac{2}{11}

(vi) 329400\dfrac{329}{400}

Answer

(i) 36100\dfrac{36}{100} = 0.36, terminating decimal expansion

(ii) 111\dfrac{1}{11}

11)0.090911)10011)229911x3210011)x3229911)x32222111)x3221111\begin{array}{l} \phantom{11)}{0.0909} \\ 11\overline{\smash{\big)}\quad100\quad} \\ \phantom{11)}\phantom{22}\underline{-99} \\ \phantom{{11}x^3-2}100 \\ \phantom{{11)}x^322}\underline{-99} \\ \phantom{{11)}{x^32222}}1 \\ \phantom{{11)}{x^322}}\overline{\phantom{1111}} \end{array}

The remainder 1 keeps repeating.
Hence, 111\dfrac{1}{11} = 0.090.\overline{09}. This is a non-terminating repeating decimal expansion

(iii) 418=3384\dfrac{1}{8} = \dfrac{33}{8}

8)4.1258)338)32 8)10888)8208168)82408840882208811111\begin{array}{l} \phantom{8)}{\enspace 4.125} \\ 8\overline{\smash{\big)}\enspace 33\quad} \\ \phantom{8)}\underline{-32\space} \\ \phantom{8)-}10 \\ \phantom{8-}\underline{-8} \\ \phantom{8)-8}20 \\ \phantom{8-}\underline{-16} \\ \phantom{8)-82}40 \\ \phantom{8-8}\underline{-40\enspace} \\ \phantom{8-822}0 \\ \phantom{8-8}\overline{\phantom{11111}} \end{array}

Hence, 4184\dfrac{1}{8} = 4.125. This is a terminating decimal expansion.

(iv) 313\dfrac{3}{13}

8)0.23076923076913)3013)26 13)408398)810013303911330333390133033178133033333120133033331171330333333330133033333)261330333333340133033333311111\begin{array}{l} \phantom{8)}{\enspace 0.230769230769} \\ 13\overline{\smash{\big)}\enspace 30\qquad\qquad\quad} \\ \phantom{13)}\underline{-26\space} \\ \phantom{13)-}40 \\ \phantom{8-}\underline{-39} \\ \phantom{8)-8}100 \\ \phantom{13303}\underline{-91\enspace} \\ \phantom{13303333}90 \\ \phantom{1330331}\underline{-78\enspace} \\ \phantom{133033333}120 \\ \phantom{13303333}\underline{-117\enspace} \\ \phantom{13303333333}30 \\ \phantom{133033333)}\underline{-26\enspace} \\ \phantom{13303333333}40 \\ \phantom{1330333333}\overline{\phantom{11111}} \end{array}

Hence, 313\dfrac{3}{13} = 0.2307690.\overline{230769}. This is a non-terminating repeating decimal expansion.

(v) 211\dfrac{2}{11}

8)0.181811)2011)11 11)908888)8)201330)111330333)901330338813303333213303311111\begin{array}{l} \phantom{8)}{\enspace 0.1818} \\ 11\overline{\smash{\big)}\enspace 20\qquad} \\ \phantom{11)}\underline{-11\space} \\ \phantom{11)-}90 \\ \phantom{8-}\underline{-88} \\ \phantom{8)-8)}20 \\ \phantom{1330)}\underline{-11\enspace} \\ \phantom{1330333)}90 \\ \phantom{133033}\underline{-88\enspace} \\ \phantom{13303333}2 \\ \phantom{133033}\overline{\phantom{11111}} \end{array}

Hence, 211=0.18\dfrac{2}{11} = 0.\overline{18}. This is a non-terminating repeating decimal expansion.

(vi) 329400\dfrac{329}{400} = 0.8225, terminating decimal expansion

400)0.8225400)3290400)3200 400)900400)2800400)2181000400)21800400)212)2000400)212000400)211110400)211111111\begin{array}{l} \phantom{400)}{0.8225} \\ 400\overline{\smash{\big)}\enspace 3290\quad} \\ \phantom{400)}\underline{-3200\space} \\ \phantom{400)-}900 \\ \phantom{400)2}\underline{-800} \\ \phantom{400)218}1000 \\ \phantom{400)21}\underline{-800} \\ \phantom{400)212)}2000 \\ \phantom{400)21}\underline{-2000\enspace} \\ \phantom{400)21111}0 \\ \phantom{400)21}\overline{\phantom{1111111}} \end{array}

Hence, 329400\dfrac{329}{400} = 0.8225. This is a terminating decimal expansion.

Number Systems - Interactive Study Notes | Bright Tutorials
BRIGHT TUTORIALS
Bright Tutorials Logo
BRIGHT TUTORIALS
CBSE Class IX | Academic Year 2026-2027
9403781999
Excellence in Education
Mathematics | Number SystemsWeb Content • Interactive Notes

Number Systems — Interactive Study Guide

Master the real number system, irrational numbers, surds, rationalisation, and exponent laws.

The Number Hierarchy

Think of numbers as nested boxes: Natural numbers are inside Whole numbers, which are inside Integers, which are inside Rational numbers, which are inside Real numbers.

Key Insight: Between any two rational numbers, there are infinitely many irrational numbers, and vice versa. The number line is “dense” with both types!

Identifying Rational vs Irrational

NumberTypeReason
√4Rational√4 = 2 (perfect square)
√7Irrational7 is not a perfect square
0.333...RationalRecurring decimal = 1/3
0.10100100010...IrrationalNon-terminating, non-recurring
πIrrationalNon-terminating, non-recurring
22/7RationalIt is p/q form (just an approximation of π)

Rationalisation — Quick Method

To rationalise a denominator with surds, multiply top and bottom by the conjugate:

  • Conjugate of (a + √b) is (a − √b)
  • Conjugate of (√a − √b) is (√a + √b)

The denominator becomes rational because (a+b)(a−b) = a² − b².

Quick Self-Check

  1. Is √(16/9) rational or irrational? (Rational: = 4/3)
  2. Simplify: √50 + √18 (= 5√2 + 3√2 = 8√2)
  3. Rationalise: 1/(√3 + 1) (= (√3 − 1)/2)
  4. Find: 81/3 (= 2)

Bright Tutorials | Hariom Nagar, Nashik Road | 9403781999 | brighttutorials.in