NCHMCT JEE 2018 Question Paper with solutions for online practice

Question : 5 of 200

Marks: +1, -0

Sapan was asked to find

7/9

of a fraction.But he made a mistake of dividing the given fraction by

7/9

and got an answer which exceeded the correct answer by

8/21

.The correct answer is ............. .

Solution:

Let fraction

=x/y

Correct answer

=x/y×7/9={7x}/{9y}

Incorrect answer

=x/y{÷}7/9=x/y×9/7={9x}/{7y}

According to the question,

{9x}/{7y}={7x}/{9y}+8/21

⇒{9x}/{7y}-{7x}/{9y}={8}/{21}

⇒{81 x-49 x}/{63 y}={8}/{21}

⇒{32 x}/{63 y}={8}/{21}

⇒32 × 21 x=8 × 63 y

⇒{x}/{y}={8 × 63}/{32 × 21}={3}/{4}

∴ Correct answer

={7x}/{9y}=7/9×3/4=7/12

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