Class 9 Maths Chapter 1: Number Systems
Class 9th maths exercise 1.1 answers
Question 1: Is zero a rational number? Can you write it in the form \(\frac{p}{q}\), where p and q are integers and q ≠ 0?
Solution:
Yes, zero is a rational number. We can express 0 as:
\[
0 = \frac{0}{1} = \frac{0}{2} = \frac{0}{-3} = \cdots
\]
Here, p = 0 and q can be any non-zero integer. This satisfies all conditions of rational numbers.
Question 2: Find six rational numbers between 3 and 4.
Solution:
Convert numbers to equivalent fractions:
\[
3 = \frac{21}{7},\quad 4 = \frac{28}{7}
\]
Six rational numbers between them:
\[
\frac{22}{7},\ \frac{23}{7},\ \frac{24}{7},\ \frac{25}{7},\ \frac{26}{7},\ \frac{27}{7}
\]
Alternatively: 3.1, 3.2, 3.3, 3.4, 3.5, 3.6
Question 3: Find five rational numbers between \(\frac{3}{5}\) and \(\frac{4}{5}\).
Solution:
Multiply numerator and denominator by 10:
\[
\frac{3}{5} = \frac{30}{50},\quad \frac{4}{5} = \frac{40}{50}
\]
Five rational numbers between them:
\[
\frac{31}{50},\ \frac{32}{50},\ \frac{34}{50},\ \frac{37}{50},\ \frac{39}{50}
\]
Simplified forms: \(\frac{31}{50},\ \frac{16}{25},\ \frac{17}{25},\ \frac{37}{50},\ \frac{39}{50}\)
Question 4: State true/false with reasons:
(i) Every natural number is a whole number.
True: Natural numbers (1,2,3…) are subset of whole numbers (0,1,2,3…)
(ii) Every integer is a whole number.
False: Negative integers (-1, -2) are not whole numbers
(iii) Every rational number is a whole number.
False: Rational numbers like \(\frac{1}{2}\) or \(-\frac{3}{4}\) aren’t whole numbers
Important Notes
- Zero is special case in number systems
- Natural numbers: Counting numbers (1,2,3…)
- To find rational numbers between two numbers: Convert to equivalent fractions
Practice Questions
1. Express \(-\frac{5}{3}\) in \(\frac{p}{q}\) form
Already in \(\frac{p}{q}\) form where p = -5, q = 3
2. Find three rational numbers between \(-\frac{1}{2}\) and \(\frac{1}{2}\)
\(-\frac{1}{4},\ 0,\ \frac{1}{4}\)
3. Is 2.333… a rational number? Justify
Yes, repeating decimal can be expressed as \(\frac{21}{9}\)
4. Write five rational numbers less than 2
1, 0, \(-\frac{1}{2}\), 1.5, \(\frac{3}{2}\)
5. True/False: All whole numbers are integers
True: Whole numbers (0,1,2…) are subset of integers