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Question

If the points P and Q represents real number \(0.7\bar 3\) and \(0.5\bar 6\)  on the number line, then what is the distance between P and Q?

This question was previously asked in
CDS I 2020 Elementary Mathematics Previous Year Paper (02-Feb-2020)
The correct answer is \(\frac{1}{6}\)

Calculating Distance Between Points on a Number Line

The question asks us to find the distance between two points, P and Q, on a number line. The points P and Q represent the real numbers \(0.7\bar 3\) and \(0.5\bar 6\) respectively. To find the distance between these points, we first need to convert the repeating decimals into fractions.

Converting Repeating Decimals to Fractions

Let's convert \(0.7\bar 3\) to a fraction:

  • Let \(x = 0.7\bar 3 = 0.7333...\).
  • Multiply by 10 to shift the decimal one place to the right: \(10x = 7.3333...\).
  • Multiply by 100 to shift the decimal past the repeating part: \(100x = 73.3333...\).
  • Subtract the equation for \(10x\) from the equation for \(100x\) to eliminate the repeating part:

\(100x - 10x = 73.3333... - 7.3333...\)

\(90x = 66\)

\(x = \frac{66}{90}\)

Simplify the fraction by dividing the numerator and denominator by their greatest common divisor, which is 6:

\(x = \frac{66 \div 6}{90 \div 6} = \frac{11}{15}\)

So, the point P represents the fraction \(\frac{11}{15}\).

Now, let's convert \(0.5\bar 6\) to a fraction:

  • Let \(y = 0.5\bar 6 = 0.5666...\).
  • Multiply by 10: \(10y = 5.6666...\).
  • Multiply by 100: \(100y = 56.6666...\).
  • Subtract the equation for \(10y\) from the equation for \(100y\):

\(100y - 10y = 56.6666... - 5.6666...\)

\(90y = 51\)

\(y = \frac{51}{90}\)

Simplify the fraction by dividing by the greatest common divisor, which is 3:

\(y = \frac{51 \div 3}{90 \div 3} = \frac{17}{30}\)

So, the point Q represents the fraction \(\frac{17}{30}\).

Calculating the Distance Between P and Q

The distance between two points on a number line is the absolute value of the difference between their coordinates. The coordinates are \(\frac{11}{15}\) for P and \(\frac{17}{30}\) for Q. The distance is \(|P - Q|\) or \(|Q - P|\). Let's calculate \(|P - Q|\):

Distance = \(|\frac{11}{15} - \frac{17}{30}|\)

To subtract these fractions, we need a common denominator. The least common multiple of 15 and 30 is 30. Convert \(\frac{11}{15}\) to an equivalent fraction with a denominator of 30:

\(\frac{11}{15} = \frac{11 \times 2}{15 \times 2} = \frac{22}{30}\)

Now substitute this back into the distance calculation:

Distance = \(|\frac{22}{30} - \frac{17}{30}|\)

Distance = \(|\frac{22 - 17}{30}|\)

Distance = \(|\frac{5}{30}|\)

The absolute value of \(\frac{5}{30}\) is \(\frac{5}{30}\). Simplify the fraction:

Distance = \(\frac{5 \div 5}{30 \div 5} = \frac{1}{6}\)

The distance between point P and point Q on the number line is \(\frac{1}{6}\).

Summary of Steps

  1. Convert the repeating decimal \(0.7\bar 3\) to the fraction \(\frac{11}{15}\).
  2. Convert the repeating decimal \(0.5\bar 6\) to the fraction \(\frac{17}{30}\).
  3. Calculate the absolute difference between the two fractions: \(|\frac{11}{15} - \frac{17}{30}|\).
  4. Find a common denominator and perform the subtraction: \(|\frac{22}{30} - \frac{17}{30}| = |\frac{5}{30}|\).
  5. Simplify the resulting fraction: \(\frac{5}{30} = \frac{1}{6}\).

Revision Table: Decimal to Fraction Conversion

Decimal Form Calculation Steps Fraction Form
\(0.7\bar 3\) \(x = 0.733...\)
\(10x = 7.333...\)
\(100x = 73.333...\)
\(90x = 66\)
\(x = \frac{66}{90}\)
\(\frac{11}{15}\)
\(0.5\bar 6\) \(y = 0.566...\)
\(10y = 5.666...\)
\(100y = 56.666...\)
\(90y = 51\)
\(y = \frac{51}{90}\)
\(\frac{17}{30}\)

Additional Information: Distance on Number Line

The distance between any two points, say 'a' and 'b', on a number line is given by the formula \(|a - b|\) or \(|b - a|\). The absolute value is used because distance is always a non-negative quantity. This concept is fundamental in understanding intervals and magnitudes on the real number line.

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