What should be subtracted from -5/7 to get -2/3?

Correct Answer is : −121-1/2121−1

Correct Answer is : −121-1/2121−1

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CTET Paper II (Mathematics and Science) Sep 2015 Solved Paper

Question : 52 of 150

Marks: +1, -0

\frac{-5}{7}

\frac{-2}{3}

Solution:

Concept:

We need to find the unknown number

x

such that subtracting it from

\frac{-5}{7}

gives

\frac{-2}{3}

Explanation:

Set up the equation:

\frac{-5}{7} - x = \frac{-2}{3}

To solve for

x

, bring

x

to one side:

\frac{-5}{7} - x + x = \frac{-2}{3} + x

gives

\frac{-5}{7} = \frac{-2}{3} + x

Now subtract

\frac{-2}{3}

from both sides:

x = \frac{-5}{7} - \frac{-2}{3}

This simplifies to

x = \frac{-5}{7} + \frac{2}{3}

Find a common denominator (21):

\frac{-5}{7} = \frac{-15}{21}

and

\frac{2}{3} = \frac{14}{21}

Add:

x = \frac{-15 + 14}{21} = \frac{-1}{21}

Thus, the required number is

\frac{-1}{21}

Answer:

\frac{-1}{21}

which matches option D.

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