All Exams Test series for 1 year @ ₹349 only
Question

If \(\frac{{\rm{a}}}{{\rm{b}}} = \frac{1}{3},\frac{{\rm{b}}}{{\rm{c}}} = 2,\frac{{\rm{c}}}{{\rm{d}}} = \frac{1}{2},\frac{{\rm{d}}}{{\rm{e}}} = 3\) and  \(\frac{{\rm{e}}}{{\rm{f}}} = \frac{1}{4}\) , then what is the value of  \(\frac{{{\rm{abc}}}}{{{\rm{def}}}}?\)

This question was previously asked in
CDS I 2020 Elementary Mathematics Previous Year Paper (02-Feb-2020)
The correct answer is \(\frac{3}{8}\)

Calculating Ratio Expressions from Given Ratios

The problem asks us to find the value of the expression \(\frac{{\rm{abc}}}}{{{\rm{def}}}}\) given several individual ratios between consecutive variables: \(\frac{{\rm{a}}}{{\rm{b}}} = \frac{1}{3}\), \(\frac{{\rm{b}}}{{\rm{c}}} = 2\), \(\frac{{\rm{c}}}{{\rm{d}}} = \frac{1}{2}\), \(\frac{{\rm{d}}}{{\rm{e}}} = 3\), and \(\frac{{\rm{e}}}{{\rm{f}}} = \frac{1}{4}\).

Understanding the Expression \(\frac{{{\rm{abc}}}}{{{\rm{def}}}}\)

The expression \(\frac{{{\rm{abc}}}}{{{\rm{def}}}}\) is a fraction with a product of three variables in the numerator and a product of three variables in the denominator. We can rewrite this expression as a product of individual ratios:

\[ \frac{{\rm{abc}}}}{{{\rm{def}}}} = \frac{{\rm{a}}}{{\rm{d}}} \times \frac{{\rm{b}}}{{\rm{e}}} \times \frac{{\rm{c}}}{{\rm{f}}} \]

Our strategy will be to calculate the values of the individual ratios \(\frac{{\rm{a}}}{{\rm{d}}}\), \(\frac{{\rm{b}}}{{\rm{e}}}\), and \(\frac{{\rm{c}}}{{\rm{f}}}}\) using the given ratios, and then multiply these values together.

Step-by-Step Ratio Calculation

Calculating \(\frac{{\rm{a}}}{{\rm{d}}}\)

We can find the ratio \(\frac{{\rm{a}}}{{\rm{d}}}\) by multiplying the consecutive ratios that link 'a' to 'd': \(\frac{{\rm{a}}}{{\rm{b}}}\), \(\frac{{\rm{b}}}{{\rm{c}}}\), and \(\frac{{\rm{c}}}{{\rm{d}}}}\).

\[ \frac{{\rm{a}}}{{\rm{d}}} = \frac{{\rm{a}}}{{\rm{b}}} \times \frac{{\rm{b}}}{{\rm{c}}} \times \frac{{\rm{c}}}{{\rm{d}}} \]

Substitute the given values:

\[ \frac{{\rm{a}}}{{\rm{d}}} = \left(\frac{1}{3}\right) \times (2) \times \left(\frac{1}{2}\right) \]

\[ \frac{{\rm{a}}}{{\rm{d}}} = \frac{1}{3} \times \frac{2}{1} \times \frac{1}{2} = \frac{1 \times 2 \times 1}{3 \times 1 \times 2} = \frac{2}{6} = \frac{1}{3} \]

So, \(\frac{{\rm{a}}}{{\rm{d}}} = \frac{1}{3}\).

Calculating \(\frac{{\rm{b}}}{{\rm{e}}}\)

We can find the ratio \(\frac{{\rm{b}}}{{\rm{e}}}\) by multiplying the consecutive ratios that link 'b' to 'e': \(\frac{{\rm{b}}}{{\rm{c}}}\), \(\frac{{\rm{c}}}{{\rm{d}}}\), and \(\frac{{\rm{d}}}{{\rm{e}}}}\).

\[ \frac{{\rm{b}}}{{\rm{e}}} = \frac{{\rm{b}}}{{\rm{c}}} \times \frac{{\rm{c}}}{{\rm{d}}} \times \frac{{\rm{d}}}{{\rm{e}}} \]

Substitute the given values:

\[ \frac{{\rm{b}}}{{\rm{e}}} = (2) \times \left(\frac{1}{2}\right) \times (3) \]

\[ \frac{{\rm{b}}}{{\rm{e}}} = \frac{2}{1} \times \frac{1}{2} \times \frac{3}{1} = \frac{2 \times 1 \times 3}{1 \times 2 \times 1} = \frac{6}{2} = 3 \]

So, \(\frac{{\rm{b}}}{{\rm{e}}} = 3\).

Calculating \(\frac{{\rm{c}}}{{\rm{f}}}\)

We can find the ratio \(\frac{{\rm{c}}}{{\rm{f}}}\) by multiplying the consecutive ratios that link 'c' to 'f': \(\frac{{\rm{c}}}{{\rm{d}}}\), \(\frac{{\rm{d}}}{{\rm{e}}}\), and \(\frac{{\rm{e}}}{{\rm{f}}}}\).

\[ \frac{{\rm{c}}}{{\rm{f}}} = \frac{{\rm{c}}}{{\rm{d}}} \times \frac{{\rm{d}}}{{\rm{e}}} \times \frac{{\rm{e}}}{{\rm{f}}} \]

Substitute the given values:

\[ \frac{{\rm{c}}}{{\rm{f}}} = \left(\frac{1}{2}\right) \times (3) \times \left(\frac{1}{4}\right) \]

\[ \frac{{\rm{c}}}{{\rm{f}}} = \frac{1}{2} \times \frac{3}{1} \times \frac{1}{4} = \frac{1 \times 3 \times 1}{2 \times 1 \times 4} = \frac{3}{8} \]

So, \(\frac{{\rm{c}}}{{\rm{f}}} = \frac{3}{8}\).

Calculating the Final Expression \(\frac{{{\rm{abc}}}}{{{\rm{def}}}}\)

Now we multiply the values of the ratios we just calculated:

\[ \frac{{\rm{abc}}}}{{{\rm{def}}}} = \frac{{\rm{a}}}{{\rm{d}}} \times \frac{{\rm{b}}}{{\rm{e}}} \times \frac{{\rm{c}}}{{\rm{f}}} \]

Substitute the calculated values:

\[ \frac{{\rm{abc}}}}{{{\rm{def}}}} = \left(\frac{1}{3}\right) \times (3) \times \left(\frac{3}{8}\right) \]

\[ \frac{{\rm{abc}}}}{{{\rm{def}}}} = \frac{1}{3} \times \frac{3}{1} \times \frac{3}{8} = \frac{1 \times 3 \times 3}{3 \times 1 \times 8} = \frac{9}{24} \]

Simplify the fraction \(\frac{9}{24}\) by dividing both the numerator and the denominator by their greatest common divisor, which is 3.

\[ \frac{9 \div 3}{24 \div 3} = \frac{3}{8} \]

So, the value of \(\frac{{\rm{abc}}}}{{{\rm{def}}}}\) is \(\frac{3}{8}\).

Given Ratio Value
\(\frac{{\rm{a}}}{{\rm{b}}}\) \(\frac{1}{3}\)
\(\frac{{\rm{b}}}{{\rm{c}}}\) \(2\)
\(\frac{{\rm{c}}}{{\rm{d}}}\) \(\frac{1}{2}\)
\(\frac{{\rm{d}}}{{\rm{e}}}\) \(3\)
\(\frac{{\rm{e}}}{{\rm{f}}}\) \(\frac{1}{4}\)
Calculated Ratio Calculation Value
\(\frac{{\rm{a}}}{{\rm{d}}}\) \(\frac{{\rm{a}}}{{\rm{b}}} \times \frac{{\rm{b}}}{{\rm{c}}} \times \frac{{\rm{c}}}{{\rm{d}}}\) \(\frac{1}{3} \times 2 \times \frac{1}{2} = \frac{1}{3}\)
\(\frac{{\rm{b}}}{{\rm{e}}}\) \(\frac{{\rm{b}}}{{\rm{c}}} \times \frac{{\rm{c}}}{{\rm{d}}} \times \frac{{\rm{d}}}{{\rm{e}}}\) \(2 \times \frac{1}{2} \times 3 = 3\)
\(\frac{{\rm{c}}}{{\rm{f}}}\) \(\frac{{\rm{c}}}{{\rm{d}}} \times \frac{{\rm{d}}}{{\rm{e}}} \times \frac{{\rm{e}}}{{\rm{f}}}\) \(\frac{1}{2} \times 3 \times \frac{1}{4} = \frac{3}{8}\)
Final Calculation Value
\(\frac{{\rm{abc}}}}{{{\rm{def}}}} = \frac{{\rm{a}}}{{\rm{d}}} \times \frac{{\rm{b}}}{{\rm{e}}} \times \frac{{\rm{c}}}{{\rm{f}}}\) \(\frac{1}{3} \times 3 \times \frac{3}{8} = \frac{3}{8}\)

Revision Table: Key Ratios and Calculations

Ratio Value
Given Ratios \(\frac{a}{b}=\frac{1}{3}, \frac{b}{c}=2, \frac{c}{d}=\frac{1}{2}, \frac{d}{e}=3, \frac{e}{f}=\frac{1}{4}\)
Intermediate Calculated Ratios \(\frac{a}{d}=\frac{1}{3}, \frac{b}{e}=3, \frac{c}{f}=\frac{3}{8}\)
Final Expression Value \(\frac{abc}{def} = \frac{a}{d} \times \frac{b}{e} \times \frac{c}{f} = \frac{1}{3} \times 3 \times \frac{3}{8} = \frac{3}{8}\)

Additional Information on Ratio Operations

When you have a series of ratios linking variables, like \(\frac{a}{b}\) and \(\frac{b}{c}\), you can find the ratio between non-consecutive variables by multiplying the intermediate ratios. For example, \(\frac{a}{c} = \frac{a}{b} \times \frac{b}{c}\). This property is used repeatedly in this problem to find ratios like \(\frac{a}{d}\) or \(\frac{b}{e}\) or \(\frac{c}{f}\).

Also, a complex fraction like \(\frac{abc}{def}\) can often be broken down into simpler fractions or products of fractions involving individual variables or pairs of variables. In this case, rewriting \(\frac{abc}{def}\) as \(\frac{a}{d} \times \frac{b}{e} \times \frac{c}{f}\) (or other combinations like \(\frac{a}{b} \times \frac{b}{c} \times \frac{c}{d} \times \frac{1}{(d/e) \times (e/f)}\) etc.) helps in utilizing the given ratios efficiently. The choice of breakdown \(\frac{a}{d} \times \frac{b}{e} \times \frac{c}{f}\) was convenient because each required ratio could be directly computed by multiplying a set of three consecutive given ratios.

Was this answer helpful?

Similar Questions

  1. What is the value of \(\sqrt[3]{{4\frac{{12}}{{125}}}}\) ?

  2. If \(\frac{{36}}{{11}} = 3\; + \;\frac{1}{{x\; + \;\frac{1}{{y\; + \;\frac{1}{z}}}}}\) , where x, y and z are natural numbers then what is (x + y + z) equal to?

  3. What is \(\frac{{{6^2} + \;{7^2} + \;{8^2} + \;{9^2} + \;{{10}^2}}}{{\sqrt {7\; + \;4\sqrt 3 \;} - \;\sqrt {4\; + \;2\sqrt 3 } }}\) equal to?

  4. In an examination, a student was asked to divide a certain number by 8. By mistake he multiplied it by 8 and got the answer 2016 more than the correct answer. What was the number?

  5. What is \(\sqrt {1 + \frac{1}{{{1^{2}}}} + \frac{1}{{{2^{2}}}}} + \sqrt {1 + \frac{1}{{{2^{2}}}} + \frac{1}{{{3^{2}}}}} + \ldots \ldots .. + \sqrt {1 + \frac{1}{{{{2007}^{2}}}} + \frac{1}{{{{2008}^{2}}}}}\) equal to?

  6. Which one among the following is the largest?

  7. If \(x\, = \,7\, + \,4\sqrt 3 \) , then what is the value of  \(\sqrt x \, + \,\frac{1}{{\sqrt x }}\) ?

  8. What is \(\rm \frac{1}{x(x-y)(x-z)}+\frac{1}{y(y-z)(y-x)}+\frac{1}{z(z-x)(z-y)}\)  equal to ?

  9. If \(x + \frac{1}{{1 + \;\frac{1}{{2 + \;\frac{1}{3}}}}} = 2,\) then what is x equal to?


Important Questions from Fractions

  1. 5 \(\frac{3}{4}\) + x + 2  \(\frac{1}{2}\) = 10  \(\frac{1}{8}\) Find the value of x.

  2. Simplify the expression 441 ÷  \(\left[270 \div \frac{3}{7}+\left(17\div \frac{1}{3}\right)-\left(8\frac{1}{2}-\frac{5}{2}\right)\right]\)

  3. Number 0.232323 can be written in rational form as:

  4. Solve: \(\frac{1}{2}\)  [{-2(2 + 3)*20}/2]

  5. Match the following.

    Column I

    Column II

    a.

    Equivalent fraction of \(\frac{7}{12}\)  is  

    i.

    Proper fraction

    b.

    Equivalent fraction of  \(\frac{9}{15}\)  is

    ii.

    Improper fraction

    c.

    \(\frac{7}{11}\)  is

    iii.

    \(\frac{21}{36}\)

    d.

    \(\frac{19}{5}\)  is

    iv.

    \(\frac{3}{5}\)

Need Expert Advice?
Test Series
CDS img
Defence
UPSC CDS 2026 Mock Test Series
536 Tests 4 Tests Free
1645 Attempts
4.3(174)
English, Hindi
More Questions from CDS

Start Your Preparation with Prepp Mobile App

Download the app from Google Play & App Store
Download the app from Google Play & App Store
Prepp Mobile App