The World of Numbers | Exercise 3.4

Question 1

Represent the rational numbers 23\dfrac{2}{3}, 54-\dfrac{5}{4} and 1121\dfrac{1}{2} on a single number line.

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Solution
Understand the Question
  • To represent rational numbers on a number line, identify which consecutive integers each number lies between:
    • 54=1.25-\dfrac{5}{4} = -1.25 lies between 2-2 and 1-1.
    • 230.67\dfrac{2}{3} \approx 0.67 lies between 00 and 11.
    • 112=32=1.51\dfrac{1}{2} = \dfrac{3}{2} = 1.5 lies between 11 and 22.
  • Divide each relevant unit interval into equal parts matching the denominator (or place by fractional distance) and plot the points.

Step 1 · Determine the Values and Intervals

Convert each rational number to find its exact or decimal value:

23=0.6660.67\dfrac{2}{3} = 0.666\dots \approx 0.67

54=1.25-\dfrac{5}{4} = -1.25

112=32=1.5\begin{aligned} 1\dfrac{1}{2} &= \dfrac{3}{2} \\[0.6em] &= 1.5 \end{aligned}

Ordering from least to greatest: 1.25<0.67<1.5    54<23<112-1.25 < 0.67 < 1.5 \implies -\dfrac{5}{4} < \dfrac{2}{3} < 1\dfrac{1}{2}

Step 2 · Plot on the Number Line

Diagram 1

  • 54-\dfrac{5}{4}: Located between 2-2 and 1-1, one-quarter of the unit distance to the left of 1-1.
  • 23\dfrac{2}{3}: Located between 00 and 11, two-thirds of the unit distance to the right of 00.
  • 1121\dfrac{1}{2}: Located between 11 and 22, exactly halfway between them.
Answer

The positions on the number line are:

  • 54-\dfrac{5}{4} lies between 2-2 and 1-1
  • 23\dfrac{2}{3} lies between 00 and 11
  • 1121\dfrac{1}{2} lies between 11 and 22
Common Mistakes
  • Negative Direction Error: Plotting 54=1.25-\dfrac{5}{4} = -1.25 between 00 and 1-1 instead of between 1-1 and 2-2. Remember that negative values move further to the left of 1-1.
  • Incorrect Interval Division: For 23\dfrac{2}{3}, divide the interval from 00 to 11 into 33 equal parts and mark the 2nd2^{\text{nd}} tick mark.

More questions in Exercise 3.4

Q1

Represent the rational numbers 23\dfrac{2}{3}, 54-\dfrac{5}{4} and 1121\dfrac{1}{2} on a single number line.

Q2

Find three distinct rational numbers that lie strictly between 12-\dfrac{1}{2} and 14\dfrac{1}{4}.

Q3

Simplify the expression: (14)+(512)\left(-\dfrac{1}{4}\right) + \left(\dfrac{5}{12}\right).

Q4

A tailor has 153415\dfrac{3}{4} metres of fine silk. If making one kurta requires 2142\dfrac{1}{4} metres of silk, exactly how many kurtas can he make?

Q5

Find three rational numbers between 3.14153.1415 and 3.14163.1416.

Q6

Can you think of other way(s) to find a rational number between any two rational numbers?

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